Internet & Web Terminology Guide

An HTTP status indicating that a request succeeded.

Example: A valid article page commonly responds with 200.

An HTTP status indicating successful creation of a resource.

Example: An API may return 201 after creating a record.

A permanent redirect status that points clients to a new URL.

Example: An old page can permanently redirect to its new address.

A redirect status commonly used for temporary redirects.

Example: A short-lived campaign URL can redirect visitors elsewhere.

A response indicating a cached representation can be reused.

Example: A browser need not download unchanged content again.

An HTTP error indicating the server cannot process the malformed request.

Example: An invalid JSON body may cause a 400 response.

An HTTP response indicating missing or invalid authentication credentials.

Example: An API can return 401 when a token is absent.

An HTTP response indicating that the server refuses to authorize the request.

Example: A user may be signed in but denied access to an admin area.

An HTTP response indicating the resource is unavailable at that address.

Example: A deleted page without a redirect may return 404.

An HTTP status indicating the server did not receive a complete request in time.

Example: An idle connection may receive a 408 response.

An HTTP status indicating a resource is intentionally no longer available.

Example: A permanently retired public document may return 410.

An HTTP status indicating valid request syntax but unprocessable instructions.

Example: An API can return 422 for invalid business-rule values.

A response scenario in which Retry-After advises when to try a request again.

Example: An API can respond 429 with Retry-After: 30.

An HTTP response indicating the client exceeded a request rate limit.

Example: An API can reply 429 after too many requests.

An HTTP response indicating the server encountered an unexpected condition.

Example: A failed backend operation may trigger 500.

An HTTP response indicating a gateway received an invalid upstream response.

Example: A proxy may return 502 if its backend malfunctions.

An HTTP response indicating a server is temporarily unable to handle requests.

Example: A service under maintenance may return 503.

An HTTP response indicating an upstream service did not respond in time.

Example: A gateway may time out while waiting for a backend.

An Ethernet standard that carries VLAN identifiers in tagged frames.

Example: A switch trunk uses 802.1Q tags for multiple VLANs.

A DNS record mapping a hostname to an IPv4 address.

Example: www.example.com may have an A record pointing to 192.0.2.10.

Comparing variants by randomly assigning users and measuring outcomes.

Example: A site tests two sign-up layouts for conversion performance.

A DNS record mapping a hostname to an IPv6 address.

Example: An AAAA record enables IPv6-capable clients to reach a host.

An HTTP request header describing media types the client prefers.

Example: A client can send Accept: application/json.

An HTTP request field listing supported content codings.

Example: A client may advertise gzip and br compression.

A device that supplies wireless connectivity to a wired or broader network.

Example: A ceiling-mounted access point provides office Wi-Fi.

A CORS response header permitting credentialed cross-origin responses.

Example: A frontend can read a credentialed response only when policies allow it.

A CORS response field naming request headers allowed in a preflight.

Example: A server can allow a custom request header during preflight.

A CORS response field listing methods allowed for a cross-origin request.

Example: A preflight response can list GET and POST.

A CORS response header identifying origins permitted to read a resource.

Example: An API may permit requests from one configured frontend origin.

Designing products so people with different abilities can use them.

Example: Proper form labels help screen-reader users.

A representation of UI semantics that browsers expose to assistive technology.

Example: A screen reader navigates headings through the accessibility tree.

A TCP flag acknowledging received sequence information.

Example: A receiver sends ACKs as TCP data arrives.

Application-Layer Protocol Negotiation, used in TLS to select a protocol.

Example: A client and server can negotiate h2 through ALPN.

A textual alternative supplied for an image in HTML.

Example: A diagram's alt text can summarize its essential meaning.

The visible text associated with a hyperlink.

Example: A link labeled DNS setup guide explains its destination.

Routing the same address from multiple locations so traffic reaches a nearby or preferred instance.

Example: Global DNS services often use anycast IP addresses.

Application Programming Interface: a defined way for software components to communicate.

Example: A weather application may request forecasts through an API.

An entry point that routes and manages requests to backend APIs.

Example: A gateway authenticates requests before sending them to services.

Authenticated Received Chain, a mechanism for preserving authentication assessment through intermediaries.

Example: A forwarding service can attach ARC sets when relaying mail.

Accessible Rich Internet Applications: roles and properties that communicate semantics to assistive technology.

Example: aria-expanded indicates whether a custom disclosure is open.

Address Resolution Protocol, which maps an IPv4 address to a link-layer address on a local network.

Example: A laptop uses ARP to locate its local gateway's MAC address.

An early packet-switching research network that contributed to the development of the internet.

Example: ARPANET connected research institutions before today's public internet.

Autonomous System Number, an identifier used by BGP routing domains.

Example: A BGP route shows the ASNs through which it was announced.

Cryptographic encryption using a public key and a corresponding private key.

Example: A sender encrypts a message to a recipient's public key.

A standardized XML-based format for publishing collections of web updates.

Example: A blog can expose an Atom feed for subscribers.

Establishing that a person or system is who it claims to be.

Example: Signing in with a password and passkey verifies identity.

A server that provides definitive DNS answers for a domain zone.

Example: The domain's authoritative server supplies its configured MX records.

Determining which actions an authenticated or other requester is allowed to perform.

Example: A regular user may not have permission to delete accounts.

An HTTP request header used to send credentials to a server.

Example: An API request can contain Authorization: Bearer ….

A network or group of networks that presents a common routing policy to the internet.

Example: A large hosting company can operate its own AS.

Automatically adding or removing computing capacity based on demand.

Example: A service starts more workers during peak traffic.

A DNS protocol operation that transfers an entire zone.

Example: An authorized secondary nameserver retrieves a zone using AXFR.

A high-capacity network carrying traffic between regions or major network segments.

Example: A carrier's backbone connects metropolitan networks.

The server-side application logic and services that support a product.

Example: Account verification often happens on the backend.

A link to a page from another website.

Example: A university article may link to a useful tutorial.

A signal or mechanism that slows producers when consumers cannot keep up.

Example: A stream pauses writes when its receiving buffer fills.

A recoverable copy of data or system state.

Example: Nightly database backups support recovery after accidental deletion.

The capacity of a network connection to carry data over time.

Example: A 100 Mbps link has a theoretical rate of 100 megabits per second.

The amount of data that can be in flight over a network path.

Example: High-RTT, high-capacity routes need enough in-flight data to fill the link.

Border Gateway Protocol, used to exchange routing information between autonomous systems.

Example: Internet providers advertise reachable IP prefixes with BGP.

Brand Indicators for Message Identification, a mechanism for publishing a brand logo for supporting mail clients.

Example: An eligible sender configures BIMI records for brand display.

A release strategy switching traffic between two parallel environments.

Example: A site routes users from the blue environment to green after verification.

A network of compromised devices under coordinated control.

Example: A botnet can generate high-volume attack traffic.

An automated notice that a message could not be delivered.

Example: An invalid recipient address can trigger a delivery failure notice.

A navigation trail showing a page's position in a site hierarchy.

Example: Home > Guides > Networking helps visitors navigate upward.

A point at which a responsive design changes its layout behavior.

Example: A grid might switch from one to three columns at a chosen width.

Traffic addressed to every station in a link-layer broadcast domain.

Example: An ARP request is broadcast on a typical IPv4 Ethernet LAN.

A hyperlink that no longer leads to its intended destination.

Example: A link to a deleted page may return 404.

A compression algorithm commonly used for web text assets.

Example: A Brotli-compressed stylesheet can transfer more efficiently.

Software that retrieves, interprets, and displays web resources.

Example: Chrome, Firefox, and Safari render HTML and run permitted JavaScript.

Temporary local storage of web resources in the browser.

Example: Cached CSS can reduce repeat-load bandwidth.

Repeatedly trying candidate passwords or keys to gain access.

Example: Rate limits and MFA reduce the success of password guessing.

A build tool that combines and transforms source modules and assets.

Example: A bundler creates optimized JavaScript files for deployment.

Fraud involving deceptive control or impersonation of business email communications.

Example: An attacker sends a forged invoice payment instruction.

Certification Authority Authorization record that limits which certificate authorities may issue certificates for a domain.

Example: A site owner can specify authorized certificate issuers.

Changing a resource identifier to force clients to fetch an updated version.

Example: A version hash in a JavaScript filename bypasses old cached copies.

A request satisfied using an existing cached copy.

Example: A CDN cache hit avoids contacting the origin server.

Replacing or removing cached data when it becomes stale or wrong.

Example: A site changes an asset filename when its CSS content changes.

A request for data not available in the relevant cache.

Example: A cache miss may require fetching content from the origin.

An HTTP header defining caching rules for responses or requests.

Example: Cache-Control: no-store tells caches not to store a response.

Storing reusable data so future requests can be served more quickly.

Example: A browser can reuse a cached logo rather than redownload it.

Gradually introducing a release to a subset of users or systems.

Example: A new version serves 5% of requests before wider rollout.

A URL declared as a preferred representative for duplicate or near-duplicate pages.

Example: A canonical link can indicate the main product URL.

A browser interface for drawing graphics with JavaScript.

Example: A drawing tool paints strokes onto a canvas element.

A web page shown before users receive broader network access.

Example: Airport Wi-Fi may require acceptance of terms on a captive portal.

Address translation by an internet provider that shares public IPv4 addresses among customers.

Example: A subscriber behind CGNAT may not have inbound port-forwarding control.

A mailbox configured to receive mail sent to otherwise unknown addresses at a domain.

Example: A domain can collect messages sent to mistyped local parts.

Content Delivery Network: distributed servers that help deliver content close to users.

Example: A CDN can cache site images at locations across the world.

An organization trusted to validate and issue digital certificates.

Example: A CA issues a certificate for a verified domain name.

The series of certificates linking a leaf certificate to a trusted root.

Example: A browser verifies intermediate certificates during TLS validation.

The process of invalidating a certificate before its original expiration.

Example: A CA revokes a compromised certificate.

Public logging of issued TLS certificates for monitoring and accountability.

Example: A site owner monitors CT logs for unexpected certificates.

Continuous Integration and Continuous Delivery/Deployment: practices for building, testing, and releasing software.

Example: A pipeline can test changes before publishing a website.

Classless Inter-Domain Routing: notation for IP network prefixes.

Example: 192.0.2.0/24 denotes a 256-address IPv4 block.

Tricking someone into interacting with a concealed or disguised page.

Example: A malicious overlay can hide a sensitive button in an iframe.

A device or program that requests a service from another system.

Example: Your browser is the client in a typical page request.

Building much of an interface in the browser using JavaScript.

Example: A dashboard fetches API data and renders its panels client-side.

On-demand access to computing infrastructure and managed services over a network.

Example: An app can run on rented cloud infrastructure.

Cumulative Layout Shift: a metric for unexpected visual movement.

Example: Images without reserved space can shift content while loading.

A collection of computing nodes managed or used together.

Example: A production cluster distributes workloads across several hosts.

A DNS record that makes one DNS name an alias of another name.

Example: shop.example.com can alias a hosted platform's hostname.

Dividing JavaScript into smaller bundles loaded when needed.

Example: A dashboard loads chart code only after its analytics tab opens.

A vulnerability where input causes unintended operating-system command execution.

Example: Passing unsanitized input to a shell command can be dangerous.

Encoding data to use fewer bytes for transmission or storage.

Example: Brotli can reduce the transfer size of text assets.

The relationship between an asset's compressed and uncompressed sizes.

Example: A text file may shrink substantially under Brotli compression.

A condition in which network demand exceeds available capacity.

Example: A busy uplink can increase queueing delays.

Reusing established connections rather than opening new ones repeatedly.

Example: An app keeps a pool of database connections.

A packaged process and its dependencies isolated using operating-system features.

Example: An app container can run consistently across environments.

A packaged filesystem and configuration used to start containers.

Example: A deployment pulls a tagged container image before starting the service.

Selecting a representation based on request information and server capabilities.

Example: A server returns WebP to a client that advertises image/webp support.

An HTTP response field identifying encodings applied to the representation.

Example: A server can send Content-Encoding: gzip for compressed content.

An HTTP field specifying the body length in bytes when applicable.

Example: A response can declare a 2048-byte payload.

A response policy restricting permitted resource loading and execution.

Example: A CSP can prevent loading scripts from unapproved sources.

An HTTP header describing the media type of the message body.

Example: Content-Type: application/json indicates JSON data.

Keeping software in a releasable state through automated processes.

Example: A pipeline produces an artifact ready for approved production release.

Automatically releasing changes that pass the delivery pipeline.

Example: A passing commit can deploy to production without manual approval.

Frequently combining code changes and running automated checks.

Example: A CI job runs tests on every pull request.

A small piece of data a site asks a browser to store and send with applicable requests.

Example: A cookie may remember an account session or preference.

An HTTP request header carrying cookies associated with a site.

Example: A session cookie can accompany subsequent requests.

A set of user-experience metrics for loading, responsiveness, and visual stability.

Example: LCP, INP, and CLS are Core Web Vitals.

Cross-Origin Resource Sharing: HTTP-based rules letting a server allow selected cross-origin browser requests.

Example: An API can allow requests from a trusted frontend origin.

A two-letter top-level domain assigned to a country or territory.

Example: .jp is Japan's country-code domain.

A search engine's practical allocation of resources for crawling a site.

Example: A large site reduces duplicate URLs to help efficient crawling.

A problem preventing a crawler from successfully retrieving an intended page.

Example: A 500 server error can interrupt a scheduled crawl.

Whether an automated crawler can discover and fetch a page.

Example: A broken internal link may prevent a crawler from reaching a resource.

Automated software that follows links or requests content for indexing or other purposes.

Example: A search crawler visits public pages to discover updates.

Testing username-password pairs stolen from other services.

Example: Reused passwords can enable takeover of unrelated accounts.

The browser work needed to turn HTML, CSS, and resources into pixels.

Example: Blocking stylesheets can delay the first render.

A response header requiring compatible cross-origin resource loading.

Example: COEP is used with COOP for some cross-origin isolation features.

A response header controlling browsing-context group isolation.

Example: COOP can help isolate a document from cross-origin windows.

A response header controlling which sites can load a resource in certain contexts.

Example: CORP can restrict cross-site embedding of sensitive resources.

Content Security Policy: a browser-enforced policy to restrict allowed content sources and behaviors.

Example: A policy can block unexpected inline script execution.

Client-Side Rendering: generating or updating much of the page in the browser with JavaScript.

Example: A frontend app may build its view after fetching JSON.

Cross-Site Request Forgery: tricking a browser into submitting an unwanted authenticated action.

Example: A forged form might attempt to alter account settings.

Cascading Style Sheets: a language describing how documents should look.

Example: CSS can style a button's color, size, and spacing.

A metric measuring unexpected visible layout shifts during a page's life.

Example: An image without dimensions can push text down and increase CLS.

Pagination using a position marker to continue through ordered data.

Example: A feed requests items after a supplied cursor.

An HTML element defined through browser custom-element APIs.

Example: A developer registers a reusable product-card element.

Common Vulnerabilities and Exposures, identifiers for publicly documented security issues.

Example: A security bulletin references a CVE identifier for a flaw.

Common Vulnerability Scoring System, a standardized severity scoring framework.

Example: A team uses a CVSS score as one factor when prioritizing fixes.

Collecting and retaining only personal data necessary for a defined purpose.

Example: A signup form avoids requesting an unnecessary date of birth.

Distributed Denial of Service, overwhelming a service using traffic from many sources.

Example: A website becomes unreachable during a large DDoS attack.

A catch-all route used when no more specific route matches.

Example: A home computer sends unknown destinations toward its gateway.

Using multiple independent security controls rather than relying on one barrier.

Example: A service combines authentication, rate limits, and network isolation.

An HTTP method requesting removal of a resource.

Example: An admin API may DELETE an obsolete record.

Software code or a library a project needs to operate.

Example: A UI library can be a dependency of a web application.

A file recording resolved dependency versions for reproducible installs.

Example: A project commits a lockfile so builds use consistent packages.

The process of releasing software or content into an environment.

Example: Publishing a new build to production is a deployment.

Dynamic Host Configuration Protocol: automatically assigns network settings to clients.

Example: A router can give a laptop an IP address and default gateway.

A signed digital document that associates a public key with an identity or name.

Example: Browsers inspect server certificates during TLS negotiation.

Inequalities in access to connectivity, devices, skills, and online services.

Example: Rural areas may experience a digital divide due to limited broadband.

A cryptographic proof that data was signed with a private key.

Example: A browser verifies a signed software package using a public key.

Plans and processes for restoring systems after major disruptions.

Example: A company tests restoring services in another region.

Tracking a request's journey across multiple services.

Example: A trace shows the checkout service waiting on inventory.

DomainKeys Identified Mail: uses cryptographic signatures to help authenticate email.

Example: A signed email can be checked using a public key from DNS.

A DMARC check relating the signing DKIM domain to the visible From domain.

Example: A DKIM signature from an unrelated domain may not satisfy DMARC.

Domain-based Message Authentication, Reporting and Conformance: a policy layer built on aligned SPF or DKIM results.

Example: A domain owner can request reporting and handling of failed messages.

A DNS record that redirects an entire subtree of domain names to another subtree.

Example: A DNAME can map names below an old domain branch to a new branch.

Domain Name System: the distributed naming system used to find records associated with domain names.

Example: A browser may look up an A or AAAA record before connecting.

A denial-of-service technique that uses larger DNS replies to magnify spoofed traffic.

Example: Attackers can abuse open resolvers that respond to spoofed source IPs.

An attack that causes a resolver to store fraudulent DNS responses.

Example: A poisoned cache can direct visitors to an attacker-controlled address.

Assigning authority for a DNS subtree to another set of nameservers.

Example: A company can delegate shop.example.com to a different DNS provider.

A query for records associated with a particular DNS name.

Example: A browser performs a DNS lookup before connecting to a new host.

Caching answers that indicate a DNS name or record does not exist.

Example: A resolver may remember NXDOMAIN until its cache lifetime expires.

Carrying DNS queries and responses over HTTPS.

Example: A browser can send DNS queries to a DoH resolver.

Transporting DNS messages over encrypted QUIC connections.

Example: A resolver can offer DoQ as an alternative encrypted transport.

Encrypting DNS traffic within a dedicated TLS connection.

Example: A privacy-focused resolver may accept queries on port 853.

A resource hint asking the browser to resolve a hostname in advance.

Example: A page pre-resolves a domain used by upcoming resources.

An informal description of the time it takes cached DNS information to expire and changes to become visible.

Example: A new A record may appear at different times across resolvers.

An attack that changes DNS answers to target internal or local network services.

Example: A hostile page may attempt to reach a private IP via DNS rebinding.

A service that queries DNS records on behalf of clients.

Example: Your device can ask a resolver for example.org's IP address.

The top of the hierarchical DNS namespace.

Example: Resolvers start from root information when following delegation paths.

A portion of the DNS namespace administered as a unit.

Example: A zone file can contain records for a domain and its subdomains.

A DNS record that publishes keys used to verify DNSSEC signatures.

Example: Validating resolvers read DNSKEY records during verification.

DNS Security Extensions: cryptographic signatures that help validate DNS data authenticity.

Example: A validating resolver can detect altered signed DNS responses.

A popular platform and tooling ecosystem for packaging and running containers.

Example: A Docker image can include a web app and its dependencies.

Document Object Model: the programming interface representing document content as nodes.

Example: JavaScript can find a heading and change its text through the DOM.

The hierarchical representation of a document's nodes exposed to scripts.

Example: JavaScript walks the DOM tree to find a button.

A human-readable name used in DNS, often for websites and email.

Example: example.org can resolve to servers hosting a site.

An organization that sells domain registrations through participating registries.

Example: You register example.com through a domain registrar.

The organization responsible for the database and operation of a particular TLD.

Example: A registry maintains delegated names under its extension.

A period when a service is unavailable or cannot perform its intended function.

Example: A database outage can cause website downtime.

Delegation Signer record linking a parent DNS zone to a child's DNSSEC key.

Example: A registrar publishes a DS record for a signed domain.

Differentiated Services Code Point, an IP header field marking traffic treatment.

Example: A managed network might mark voice packets with a DSCP value.

Running IPv4 and IPv6 simultaneously on a network or device.

Example: A website can be reached through either address family.

The ability to send and receive data, either simultaneously or in alternating directions.

Example: Full-duplex Ethernet can transmit in both directions at once.

Substantially similar content accessible at multiple URLs.

Example: Print and standard article URLs may show the same story.

Encrypted Client Hello, a TLS mechanism that conceals sensitive ClientHello information when supported.

Example: ECH can obscure a visited hostname from some on-path observers.

A content cache located near end users or network edges.

Example: A CDN edge cache stores popular images locally.

Running computation near users or data sources rather than only in centralized regions.

Example: An edge function can modify a response at a nearby point of presence.

An identifier for a mailbox or delivery destination, commonly formatted local-part@domain.

Example: [email protected] is a typical email address.

An additional address that forwards or delivers into an existing mailbox.

Example: An employee receives mail sent to sales@ and hello@ aliases.

Forging message identity information to impersonate another sender.

Example: An attacker crafts a message that appears to come from a trusted contact.

Grouping related messages into a conversation.

Example: A client groups replies using message references and subject information.

Transforming readable data into a protected form using cryptographic methods.

Example: TLS encrypts traffic so intermediaries cannot ordinarily read it.

A specific address or interface through which a service is accessed.

Example: /api/products can be an API endpoint.

The sender address used in SMTP transport, separate from the visible From header.

Example: Bounce notifications are directed to the SMTP envelope sender.

The allowed amount of unreliability under a service objective.

Example: A team slows releases after using most of its error budget.

A validator identifying a version of a resource representation.

Example: A browser can send If-None-Match with an earlier ETag.

A family of technologies for carrying frames on wired local networks.

Example: A desktop computer connects to a switch with an Ethernet cable.

Navigation that filters collections through multiple attributes.

Example: An online store filters products by size, color, and brand.

Moving service operation to an alternate instance or location after failure.

Example: Traffic switches to a secondary database after primary failure.

A small icon representing a website in tabs or bookmarks.

Example: A site can provide a favicon in its document head.

A setting that enables or disables application behavior without a full code release.

Example: A team enables a new checkout flow for a small group of users.

A cable that transmits information as pulses of light through glass or plastic.

Example: A long-distance network may use fiber for high throughput.

Standards for phishing-resistant public-key authentication using security keys or platform authenticators.

Example: A passkey login can use FIDO2 technology.

A TCP flag indicating that a sender has finished sending data.

Example: An orderly TCP connection shutdown uses FIN segments.

A security control that allows or blocks network traffic according to rules.

Example: A firewall may block unsolicited connections to a server.

A policy that permits or blocks traffic based on defined conditions.

Example: A rule might permit HTTPS while rejecting unsolicited inbound traffic.

The time when the browser first displays text or image content.

Example: A fast FCP gives visitors an early sign that a page is loading.

Controlling keyboard focus during interface changes.

Example: A modal moves focus inside itself when opened.

A CSS descriptor controlling font rendering during web-font loading.

Example: font-display: swap can show fallback text before the custom font loads.

A server that makes requests on behalf of clients.

Example: An enterprise forward proxy enforces outbound browsing rules.

Dividing a large packet or data object into smaller pieces for transport.

Example: An oversized IPv4 packet may be fragmented if permitted.

A link-layer data unit with addressing and integrity information.

Example: An Ethernet frame transports an IP packet over a local link.

The user-facing portion of a website or app, commonly rendered in the browser.

Example: Navigation bars and interactive forms belong to the frontend.

Describes work spanning both frontend and backend development.

Example: A full-stack developer may create UI and API endpoints.

A cloud service that runs event-triggered functions on demand.

Example: An uploaded image can trigger a resize function.

A device or software route used to reach another network.

Example: A laptop sends internet-bound traffic through its default gateway.

A top-level domain that is not a country-code TLD.

Example: .com and .museum are generic TLDs.

An HTTP method used to request a representation of a resource.

Example: Opening a page usually results in a GET request.

A distributed version-control system for tracking changes in files.

Example: Developers create commits to record revisions.

Address information stored in a parent zone to bootstrap delegated nameservers.

Example: A parent zone provides glue when a child nameserver is inside its own domain.

A query language and runtime for APIs in which clients specify desired data fields.

Example: A client requests a product title and price through GraphQL.

Generic Routing Encapsulation, a protocol used to tunnel other network traffic.

Example: Two routers can carry encapsulated packets through a GRE tunnel.

A spam-control technique that temporarily rejects unfamiliar sending combinations.

Example: A legitimate sender's retry may succeed after an initial delay.

A high-performance remote procedure call framework often using Protocol Buffers.

Example: Microservices exchange typed messages using gRPC.

A widely supported compression format used for HTTP content encoding.

Example: A server may send compressed HTML with gzip.

A specialized device for protecting and using cryptographic keys.

Example: A certificate authority stores sensitive signing keys in an HSM.

A function mapping data to a fixed-size digest, commonly used for integrity checks.

Example: A download page may publish a SHA-256 file digest.

Computing a fixed-format digest from input data using a hash function.

Example: A checksum can reveal accidental file changes.

An HTTP method that requests the response headers without the body.

Example: A client can inspect a file's content type before downloading.

Delays caused when work at the front of a queue holds up later work.

Example: Packet loss on one TCP stream can delay other data sharing that transport.

A test for whether a system or service is functioning or ready.

Example: A load balancer removes an unhealthy instance from rotation.

Hash-based Message Authentication Code, which verifies integrity with a shared secret.

Example: An API signs a webhook payload with HMAC.

The entry page commonly shown at the root of a website.

Example: Visiting example.com may load the site's homepage.

One forwarding step through a network router or intermediate node.

Example: A traceroute can show multiple hops on the way to a server.

Increasing capacity by adding more machines or instances.

Example: A web app may add several identical servers.

The service of providing computing and storage resources to serve a website.

Example: A host stores site files or runs web application software.

HTTP Strict Transport Security: a policy telling browsers to use HTTPS for future connections.

Example: A site can send Strict-Transport-Security to discourage HTTP downgrades.

HyperText Markup Language: markup that describes the structure and meaning of web content.

Example: <h1> gives text heading semantics.

An inert markup fragment intended for cloning and later insertion.

Example: A script clones a template to add another result card.

Hypertext Transfer Protocol: an application protocol for requesting and transferring web resources.

Example: GET /index.html asks a server for a document.

Storing response representations so later requests can reuse them.

Example: A browser cache serves an unchanged logo without fetching it again.

A field that carries metadata about a request or response.

Example: Content-Type tells the client what type of content it received.

A verb describing what an HTTP request intends to do.

Example: GET retrieves; POST commonly submits data.

A message sent by a client asking a server to perform an action or return data.

Example: A GET request can fetch a product listing.

A message from a server containing status, headers, and often a body.

Example: A 200 response may contain HTML for a page.

A three-digit number identifying the outcome of an HTTP request.

Example: 404 indicates the requested resource was not found.

An early HTTP version that commonly used one request per TCP connection.

Example: An old client may send an HTTP/1.0 request without persistent connections.

An HTTP version supporting persistent connections and standardized host identification.

Example: Many servers still accept HTTP/1.1 requests.

An HTTP version that multiplexes streams over one connection and compresses headers.

Example: A page can load several resources concurrently over HTTP/2.

An HTTP version that runs over QUIC instead of TCP.

Example: A browser can load a site over HTTP/3 when available.

A cookie attribute that prevents access through ordinary client-side JavaScript.

Example: An HttpOnly session cookie is not available via document.cookie.

HTTP carried over an authenticated encrypted TLS connection.

Example: The browser protects a login request in transit using HTTPS.

A DNS SVCB-family record advertising HTTPS endpoint parameters.

Example: An HTTPS record can advertise HTTP/3 support to clients.

An older networking device that repeats incoming signals to multiple ports.

Example: Ethernet hubs have largely been replaced by switches.

Attaching client-side behavior to server-rendered HTML.

Example: A JavaScript framework hydrates an already visible page.

A reference that lets users navigate to another resource or location.

Example: The text in an HTML anchor can take visitors to a documentation page.

Text containing connections to other resources or sections.

Example: A glossary can link technical words to their definitions.

Software or firmware that creates and manages virtual machines.

Example: A hypervisor assigns memory and CPU resources to guest systems.

Internet Assigned Numbers Authority, coordinator of several global protocol registries and identifier functions.

Example: IANA maintains registries for DNS and protocol parameters.

Internet Corporation for Assigned Names and Numbers, which coordinates parts of the internet's naming systems.

Example: ICANN oversees policies affecting generic top-level domains.

Internet Control Message Protocol, used for IP network errors and diagnostic messages.

Example: A ping utility commonly sends ICMP echo requests.

The IPv6 version of ICMP, also used for essential network control functions.

Example: Neighbor Discovery messages use ICMPv6.

A property where repeating an operation has the same intended effect as doing it once.

Example: Repeated PUT requests can replace a resource with identical content.

Internationalized Domain Name, a domain using supported non-ASCII characters.

Example: A user can register a domain displayed with accented letters.

Internationalized Domain Names in Applications, protocols for using internationalized domain labels.

Example: Browsers apply IDNA processing to supported Unicode domain names.

Institute of Electrical and Electronics Engineers, a professional body publishing technical standards.

Example: IEEE 802.11 defines a family of wireless networking standards.

Internet Engineering Task Force, an open standards community developing internet technical documents.

Example: IETF working groups discuss new protocol specifications.

A conditional request field specifying a modification time.

Example: A client can request an unchanged file without downloading its body again.

A conditional request field comparing entity-tag validators.

Example: A server can return 304 when the ETag matches.

An HTML element that embeds another browsing context within a page.

Example: A map or video player can be embedded using an iframe.

An HTML attribute listing image candidates at different sizes or densities.

Example: A browser picks a suitable image file using srcset.

Internet Message Access Protocol: allows clients to access and synchronize stored email.

Example: A mail app can keep folders aligned using IMAP.

An IMAP feature that lets the server notify clients of mailbox changes.

Example: A mail app uses IDLE to learn when a new message arrives.

Organized detection, management, and recovery during service problems.

Example: On-call engineers triage a production outage.

An overview of which discovered site URLs are indexed or excluded.

Example: A site owner reviews coverage after publishing many new pages.

Whether a page can be included in a search engine's index under applicable conditions.

Example: A page blocked by noindex is not intended for indexing.

A browser database for storing structured data locally.

Example: An offline note app saves documents in IndexedDB.

Organizing discovered content so it can be retrieved in search systems.

Example: A page may be crawled but not selected for indexing.

Cloud services providing virtualized compute, storage, and networking resources.

Example: A team rents virtual machines through an IaaS provider.

Managing infrastructure through versioned machine-readable definitions.

Example: A repository stores definitions for cloud networks and servers.

Interaction to Next Paint: a responsiveness metric based on interactions during a page visit.

Example: Slow input handlers may worsen INP.

A responsiveness metric reflecting delays from user interactions to visual updates.

Example: Heavy main-thread work can worsen INP during typing.

A certificate signed by a higher authority and used to issue other certificates.

Example: A website's certificate is commonly issued by an intermediate CA.

A link pointing to another page on the same website.

Example: A glossary can link from DNS to its DNS record guide.

A global network of interconnected networks that exchange data using the Internet Protocol suite.

Example: An email and a website can travel across different networks without using the same application.

A facility where independent networks exchange internet traffic.

Example: An IXP can reduce the distance traffic travels between local providers.

The processes and institutions shaping internet operation and policy.

Example: Technical and policy communities discuss naming and routing governance.

A nonprofit organization supporting an open, globally connected internet.

Example: ISOC supports internet education and policy initiatives.

The ability of independently developed systems to work together.

Example: An email sent between different providers relies on interoperability.

Research concepts for networking over long delays and disruption across space.

Example: Deep-space communication requires techniques tolerant of long round trips.

A browser API reporting when an element intersects a viewport or root.

Example: An image loads when it approaches the visible screen.

A numeric network address used to identify a network interface or endpoint.

Example: 192.0.2.10 is an example IPv4 address reserved for documentation.

The widely used 32-bit version of Internet Protocol addressing.

Example: An IPv4 address contains four decimal octets.

The newer 128-bit Internet Protocol addressing system.

Example: 2001:db8::1 is a documentation IPv6 address.

Intermediate System to Intermediate System, a link-state routing protocol used by many networks.

Example: A service provider may use IS-IS inside its backbone.

International Organization for Standardization, which publishes international technical standards.

Example: ISO publishes standards for country codes and information security.

An incremental DNS zone-transfer operation that transfers changes since a known serial.

Example: IXFR can reduce bandwidth when only a few records change.

A programming language used in browsers and servers for interactive behavior.

Example: JavaScript can update search results as someone types.

Variation in packet arrival times or latency.

Example: Video calls can sound unstable when jitter is high.

JavaScript Object Notation: a text format for structured data exchange.

Example: An API can return {"name":"Alex"} as JSON.

A vocabulary for describing and validating JSON data structures.

Example: An API validates a payload against a JSON Schema.

A JSON-based syntax commonly used to embed linked data in web pages.

Example: A site includes JSON-LD describing its organization.

JSON Web Token: a compact structure for transmitting claims, commonly signed.

Example: An API may accept a short-lived JWT access token.

A mechanism for keeping connections open for additional messages or detecting peers.

Example: Persistent HTTP/1.1 connections avoid repeated connection setup.

Processes for creating, storing, controlling, and retiring cryptographic keys.

Example: A system stores encryption keys apart from its database.

Replacing cryptographic keys according to policy or security needs.

Example: A service rotates API signing keys without stopping requests.

A word or phrase used in a search or content analysis context.

Example: A user might search for “what is DNS”.

A platform for deploying and managing groups of containerized workloads.

Example: A cluster can automatically restart failed application containers.

A web performance metric measuring when the largest visible content element is rendered.

Example: A large hero image can determine a page's LCP.

The access connection between a provider's network and the end user.

Example: A fiber connection delivers the last mile to a home.

An HTTP response field indicating a resource's modification timestamp.

Example: A browser may use Last-Modified for cache revalidation.

The time delay between sending a request and receiving a response or signal.

Example: A faraway server may add noticeable latency.

Deferring nonessential resources until they are likely to be needed.

Example: Offscreen images can load when approaching the viewport.

Largest Contentful Paint: a metric measuring when the largest eligible content element becomes visible.

Example: A large hero image may determine a page's LCP.

Granting only the permissions needed for a task.

Example: A reporting service receives read-only database access.

An SEO term for ranking value that can pass through links in some search systems.

Example: Internal linking can help important pages gain prominence.

An email header offering machine-readable unsubscribe methods.

Example: A mail app may display a built-in unsubscribe control.

A check indicating whether an application process should be restarted.

Example: A stuck service fails its liveness probe and is restarted.

A system that distributes incoming requests across multiple servers.

Example: A busy site spreads traffic over several backend instances.

A browser API for persisting small string key-value data by origin.

Example: A site remembers a theme preference in localStorage.

A hostname conventionally resolving to the local machine.

Example: A developer may preview a local service at localhost:3000.

Recording events generated by software or infrastructure.

Example: A server log records errors and request metadata.

A technique in which clients keep requests open until updates are available.

Example: A chat client can repeatedly issue long-poll requests.

Main-thread work lasting long enough to delay other interactions.

Example: A large synchronous calculation becomes a long task.

An address that refers back to the local computer.

Example: 127.0.0.1 points to the local IPv4 host.

A link-layer identifier assigned to a network interface, commonly 48 bits long.

Example: A switch learns which port is associated with a source MAC address.

Software that delivers received mail into the recipient's mailbox.

Example: An MDA files accepted messages into mailbox storage.

Software that receives and transfers email between servers.

Example: An MTA queues a message until the destination mail server responds.

Software through which a person composes and reads email.

Example: A desktop email application is an MUA.

A configured limit on storage used by a mailbox.

Example: Messages may be rejected when a mailbox reaches its quota.

A service distributing messages to a subscribed group.

Example: A project announcement list emails all subscribers.

The browser thread that handles most document parsing, script execution, and interactions.

Example: Heavy JavaScript on the main thread can delay clicks.

Software designed to cause harm or carry out unauthorized activity.

Example: A disguised download can contain malicious code.

A CSS condition that applies styles based on device or user preferences.

Example: A media query can stack columns on narrow screens.

An email header containing an identifier for a particular message.

Example: Email clients use Message-ID values to track conversations.

An HTML metadata value summarizing a page, sometimes used as search snippet text.

Example: A useful description can explain what a guide contains.

A numerical measurement tracked over time.

Example: Requests per second is a service metric.

An architecture that splits an application into independently deployable services.

Example: An online store may have separate checkout and catalog services.

Multipurpose Internet Mail Extensions: standards for representing content types and attachments in messages.

Example: MIME identifies whether content is plain text, HTML, or an attachment.

Reducing source-file size by removing unnecessary formatting and renaming safely.

Example: Minified JavaScript usually downloads faster than verbose source.

Equipment that adapts signals for a particular access connection.

Example: A cable modem connects a home to a cable internet provider.

An application architecture with major functions deployed as a single unit.

Example: A small web app may start as one monolithic deployment.

Multiprotocol Label Switching, forwarding technology based on short labels.

Example: A provider may use MPLS to manage traffic across its backbone.

Maximum Segment Size, the largest TCP data payload advertised for a connection.

Example: TCP peers negotiate an MSS to fit available packet sizes.

Maximum Transmission Unit, the largest network-layer payload a link can carry without fragmentation.

Example: An Ethernet network often uses an IP MTU of 1500 bytes.

Authentication requiring factors from different categories.

Example: A password and security key provide different factors.

A website whose navigation commonly loads distinct documents from the server.

Example: A news site serves a fresh HTML page for each article.

Communication delivered to a subscribed group of receivers.

Example: Some local discovery protocols use multicast announcements.

A browser API reporting changes to a DOM subtree.

Example: A widget watches for newly inserted elements.

TLS authentication in which client and server both present certificates.

Example: Internal services use mTLS to authenticate one another.

A DNS record indicating where mail for a domain should be delivered.

Example: Email to [email protected] follows the domain's MX records.

A DNS server that answers queries, often for a specific zone.

Example: NS records delegate a domain to its authoritative nameservers.

A DNS record containing rewrite rules for service discovery and identifiers.

Example: Some SIP deployments use NAPTR records to locate services.

Network Address Translation: rewriting address information as traffic crosses a router.

Example: A home router commonly shares one public IPv4 address across devices.

An IPv6 mechanism for discovering neighbors, routers, and link-layer addresses.

Example: An IPv6 host learns its gateway through router advertisements.

The policy principle that internet access providers should treat traffic without improper discrimination.

Example: Debates around blocking and paid prioritization concern net neutrality.

A phenomenon where a service becomes more useful as participation grows.

Example: A messaging network may gain value when more contacts join it.

Hardware or a virtual endpoint used to send and receive network traffic.

Example: A laptop can have separate Ethernet and wireless interfaces.

Dividing a network into separate security or management zones.

Example: Guest devices are isolated from internal company systems.

The neighboring router or destination to which a packet is forwarded.

Example: A route table may list an ISP router as the next hop.

A computing instance participating in a distributed system or cluster.

Example: A Kubernetes worker node runs application pods.

A directive asking cooperating search engines not to index a page.

Example: A private staging page may use a noindex directive.

A package registry and command-line tooling widely used in JavaScript development.

Example: A project installs a dependency with npm.

A DNS record naming the servers authoritative for a delegated DNS zone.

Example: The parent zone lists the child's NS servers.

A DNSSEC record supporting authenticated denial of existence.

Example: An NSEC response can prove that a requested name does not exist.

A DNSSEC denial-of-existence record using hashed DNS names.

Example: NSEC3 can reduce straightforward enumeration of signed-zone names.

A DNS response code indicating that a queried domain name does not exist.

Example: A typo in a hostname can produce an NXDOMAIN answer.

An authorization framework allowing clients to obtain scoped access to resources.

Example: A photo app can be authorized to access selected account data.

Understanding system behavior using telemetry such as logs, metrics, and traces.

Example: Engineers inspect latency metrics and traces to investigate slow requests.

Online Certificate Status Protocol, a method for checking certificate revocation status.

Example: Some clients use OCSP responses to assess certificate status.

Metadata convention helping social platforms represent shared links.

Example: og:title can specify a shared page's headline.

A redirect that accepts untrusted destinations without appropriate restrictions.

Example: An attacker may use a trusted site's redirect endpoint in phishing links.

Software whose license permits inspection, modification, and redistribution under its terms.

Example: A developer contributes fixes to an open-source web server.

A technical specification developed and available under broadly accessible conditions.

Example: Open protocols allow different vendors' software to interoperate.

A specification for describing HTTP APIs in a machine-readable form.

Example: A team generates API documentation from an OpenAPI document.

An identity layer built on OAuth 2.0 that supports user authentication.

Example: A site can use OIDC for sign-in through an identity provider.

Equipment that terminates a fiber connection at a subscriber's premises.

Example: An ONT connects a home fiber line to local networking equipment.

An HTTP method for requesting communication options for a target resource.

Example: Browsers use OPTIONS for some CORS preflight requests.

Coordinated automation for deployment, scaling, and lifecycle management.

Example: An orchestrator replaces crashed application instances.

Unpaid listings in search results, distinct from sponsored placements.

Example: A documentation article may appear as an organic result.

A web security boundary usually defined by scheme, hostname, and port.

Example: https://example.com and http://example.com have different origins.

An HTTP request field identifying the origin initiating a request.

Example: A browser includes Origin in many CORS-related requests.

The upstream server providing original content to intermediaries.

Example: A CDN fetches an uncached article from the origin server.

A page with no discoverable internal links pointing to it.

Example: A published tutorial hidden from all navigation can become orphaned.

Open Shortest Path First, a link-state interior routing protocol.

Example: Enterprise routers use OSPF to discover internal network routes.

Software that installs, updates, and manages dependencies.

Example: A developer installs project libraries using a package manager.

A unit of data carried by a packet-switched network.

Example: A large download is transmitted using many packets.

The failure of transmitted packets to reach their destination.

Example: High loss can produce choppy calls or slow transfers.

Splitting large collections into smaller batches or pages.

Example: An API returns 50 products at a time with a next-page cursor.

A phishing-resistant sign-in credential built on public-key cryptography.

Example: A device can sign you in without a reusable password.

Trying a few common passwords across many accounts.

Example: An attacker may test one password against a large employee list.

An HTTP method for applying partial modifications to a resource.

Example: An API can PATCH a single profile field.

A technique for learning the largest packet size a route can support.

Example: A server can reduce packet size after receiving a packet-too-big signal.

Accessing unintended files by manipulating file paths.

Example: An unsafe download endpoint may allow ../ segments to escape its directory.

A connection arrangement in which networks exchange traffic directly.

Example: Two providers peer at an internet exchange point.

A response policy controlling access to selected browser features.

Example: A site can restrict camera access through Permissions-Policy.

An attempt to deceive people into revealing information or taking unsafe actions.

Example: A fake login page may imitate a familiar company.

A utility commonly used to measure network reachability and round-trip time with ICMP.

Example: ping example.com can help diagnose connectivity.

A managed platform for deploying applications without handling all server operations.

Example: A developer pushes application code to a PaaS service.

The smallest deployable workload unit in Kubernetes, containing one or more containers.

Example: Two closely related containers can share networking inside a pod.

Code that supplies a missing API or behavior in an older environment.

Example: An app loads a polyfill when a target browser lacks a feature.

Post Office Protocol version 3: a protocol for retrieving mail, often by downloading messages.

Example: A mail client may use POP3 to collect inbox messages.

A number identifying a transport-layer service on a host.

Example: HTTPS normally uses TCP port 443.

A router rule mapping incoming traffic to an internal host and port.

Example: A developer forwards a test service to a machine on a home LAN.

An HTTP method for submitting data for processing.

Example: A registration form may send its fields using POST.

A review of an incident's causes, impact, and improvement actions.

Example: A team documents lessons from a database outage.

A resource hint encouraging early connection setup to an origin.

Example: A page preconnects to an asset host before requesting files.

A resource hint suggesting the browser fetch likely future resources.

Example: A site prefetches assets for the next likely page.

A browser's OPTIONS request checking permission for certain cross-origin requests.

Example: A custom authorization header can trigger a CORS preflight.

A resource hint that prioritizes fetching a resource needed soon.

Example: A page preloads its main display font.

An address reserved for local networks, generally not routed on the public internet.

Example: 192.168.1.1 is common on home networks.

The secret component of a cryptographic key pair.

Example: A server must protect its TLS private key from disclosure.

The live environment serving real users.

Example: A bug affecting the production site impacts visitors.

A web application using web capabilities to provide app-like experiences.

Example: A PWA can be installed and may work offline.

Software distributed under terms that usually restrict modification or redistribution.

Example: A commercial server tool may have a proprietary license.

A structured data serialization format with schemas and generated bindings.

Example: A backend encodes a message using a .proto definition.

An intermediary that forwards requests or responses on behalf of clients.

Example: A corporate proxy can filter outbound web traffic.

A DNS record used for reverse DNS to associate an address with a hostname.

Example: Mail servers sometimes inspect the PTR name of a sender's IP.

An address intended to be globally routable on the public internet.

Example: A hosted server can have a public IP address.

The shareable part of a cryptographic key pair.

Example: A recipient can use a public key for supported encryption schemes.

Cryptographic techniques using a related public and private key pair.

Example: A server signs data with its private key for verification by a public key.

An encoding used with IDNA to represent Unicode domain labels using ASCII.

Example: An international domain label can appear as an xn-- name.

An HTTP method that creates or replaces a resource representation at a target URI.

Example: An API can use PUT to replace a profile document.

Progressive Web App: a web app enhanced with features such as installation and offline capabilities.

Example: A PWA can cache essential resources for offline use.

Quality of Service techniques for prioritizing or managing traffic on a network.

Example: A router can prioritize voice packets over background downloads.

The purpose a person hopes to accomplish with a search.

Example: A query like how to change DNS suggests informational intent.

A transport protocol built on UDP with encryption and multiplexed streams.

Example: Modern browsers use QUIC to communicate with HTTP/3 servers.

Malicious software that disrupts access to data or systems, often demanding payment.

Example: A ransomware incident may encrypt shared files.

Restricting how frequently clients may perform operations.

Example: An API permits 100 requests per minute per account.

Registration Data Access Protocol, a structured successor for many internet registration lookups.

Example: A domain-information service retrieves registration data through RDAP.

A check determining whether an application should receive traffic.

Example: A pod stays unready until its database connection is established.

An email header added by mail servers to record message transit.

Example: A troubleshooting engineer reads Received lines to inspect a delivery route.

The targeted maximum amount of data loss measured in time.

Example: An RPO of 15 minutes requires sufficiently frequent replication or backups.

The targeted maximum time to restore a service after disruption.

Example: An RTO of two hours guides recovery planning.

A DNS server that follows the lookup process and returns a result to its requester.

Example: A recursive resolver may cache a recently requested record.

A server or browser mechanism that sends visitors to a different address.

Example: A renamed article can redirect its old URL to the new one.

An HTTP field indicating the page address from which a request was initiated.

Example: A navigation may include a Referer header with a source URL.

An HTTP field or document policy controlling referrer information disclosure.

Example: A site can limit cross-site referrer details using strict-origin-when-cross-origin.

An HTML link relation indicating a preferred canonical URL.

Example: A page uses rel=canonical to signal its primary version.

A resource that delays rendering until it is processed.

Example: A synchronous stylesheet in the head can block initial painting.

Keeping copies of data or services synchronized across locations.

Example: A database replicates changes to a standby node.

An email header specifying where replies should be directed.

Example: A support newsletter sends responses to a helpdesk address.

A managed location for project files and version history.

Example: A Git repository tracks code changes across commits.

A browser API that reports changes to an element's rendered dimensions.

Example: A chart redraws when its container is resized.

An approach that adapts layouts to different screens and capabilities.

Example: A desktop two-column layout can stack on a phone.

Serving an appropriately sized or formatted image for the user's device.

Example: A phone can receive a smaller photo than a desktop monitor.

An architectural style for networked systems using resources and a uniform interface.

Example: A REST-style API might expose /articles/42.

A header generally recording the SMTP envelope sender after delivery.

Example: A delivered message can show a Return-Path address for bounces.

A server that accepts requests for backend services and forwards them appropriately.

Example: A reverse proxy can route requests to several app servers.

Request for Comments, a publication series documenting internet protocols and related topics.

Example: A developer reads an RFC for the details of an HTTP extension.

An enhanced search listing using eligible structured or extracted information.

Example: A recipe result may show cooking time and ratings where supported.

Routing Information Protocol, an older distance-vector routing protocol.

Example: RIP selects routes using hop count rather than link bandwidth.

Regional Internet Registry, an organization allocating IP address resources within a region.

Example: Network operators request address resources through their RIR.

A text file defining crawler access rules for a host.

Example: A site's robots.txt can discourage crawling certain paths.

Restoring a prior application version after a problematic release.

Example: Operators roll back when a deployment causes errors.

A trusted certificate used as an anchor for certificate-chain validation.

Example: Operating systems include trusted root certificates.

A server authoritative for the DNS root zone.

Example: A resolver asks a root server which nameservers handle a TLD.

The duration for a message to travel to a destination and for a response to return.

Example: A higher RTT can slow repeated network handshakes.

A device's collection of forwarding destinations and next hops.

Example: A router checks its route table before sending a packet onward.

A device that forwards network packets between networks.

Example: A home router connects the local network to an internet provider.

A DNSSEC record containing a digital signature over a DNS record set.

Example: An RRSIG helps confirm that an answer was signed by a zone key.

Really Simple Syndication: an XML-based format for publishing update feeds.

Example: A reader can subscribe to new posts through an RSS feed.

A TCP flag used to reset or abort a connection.

Example: A closed TCP port may respond with a reset.

Step-by-step operational instructions for recurring situations.

Example: A runbook describes how to restart a failed service safely.

A method defined as not requesting a state change at the server.

Example: GET is a safe HTTP method even though logging may still occur.

A browser security mechanism limiting how documents from different origins interact.

Example: An unrelated page cannot freely read another site's response.

A cookie attribute that restricts when cookies are sent with cross-site requests.

Example: SameSite=Lax can reduce some cross-site request risks.

Security Assertion Markup Language, an XML-based federated identity standard.

Example: An enterprise uses SAML for single sign-on to a business app.

A system's ability to handle changes in workload by growing or adapting resources.

Example: A service can add workers as demand increases.

A shared vocabulary often used to describe structured data on the web.

Example: Article and Organization are Schema.org types.

Software-Defined Wide Area Networking, centrally managed routing across multiple connections.

Example: A branch office can switch between broadband and private links.

A webmaster interface for inspecting search indexing and performance data.

Example: A publisher checks reports for pages excluded from indexing.

A service that discovers, indexes, and helps people find relevant web content.

Example: A search query can return pages from many different domains.

The goal a person likely has when entering a search query.

Example: “How to clear cache” usually seeks instructions.

The ordering of results for a particular search query.

Example: Different searches can produce different result orders.

The title and description-like preview shown for a search result.

Example: A clear page summary may influence the snippet displayed.

A fetch-metadata request header indicating the request's mode.

Example: Navigation requests typically have a navigate mode.

A fetch-metadata request header describing a request's site relationship.

Example: A server can distinguish same-origin from cross-site fetches.

A cookie marked Secure, restricting transmission to secure contexts with specific exceptions.

Example: Session cookies should generally use the Secure attribute.

Using HTML elements according to the meaning of their content.

Example: <nav> identifies a navigation section rather than just a generic box.

A convention for software versions using major, minor, and patch numbers.

Example: Version 2.1.3 indicates a patch release under semantic versioning.

Search Engine Results Page: the page showing results for a search query.

Example: A SERP may include organic listings and rich results.

A specialized module or presentation format on a search results page.

Example: A result page can include maps, video panels, or answer boxes.

A system that provides a service or resource to clients.

Example: An API server can respond with JSON.

A browser-friendly mechanism for a server to push a stream of events over HTTP.

Example: A live dashboard can subscribe to updates via SSE.

Caching results or content on a server for faster delivery.

Example: An app can cache a popular product listing.

Generating a page's HTML on a server for a request.

Example: A server renders product details before sending the response.

A cloud execution model where infrastructure management is abstracted and capacity often scales automatically.

Example: A function can run when an HTTP request arrives.

A DNS response indicating that a server could not complete a query.

Example: A validation problem can cause a recursive resolver to return SERVFAIL.

A browser script that runs separately from pages and can intercept certain network requests.

Example: A service worker can support offline caching.

A maintained state connecting related interactions for a user or client.

Example: A signed-in browser session can persist across requests.

An attack that tricks a user into authenticating with an attacker-known session identifier.

Example: A site should issue a fresh session identifier after login.

Taking control of another user's authenticated session.

Example: A stolen session token may let an attacker impersonate a user.

Browser key-value storage scoped to a page session and origin.

Example: A multistep form keeps temporary state in sessionStorage.

An HTTP response header asking the client to store a cookie.

Example: A server can set a session identifier with expiry options.

A cryptographic hash algorithm producing a 256-bit digest.

Example: A tool computes SHA-256 to check whether a file changed.

A web platform feature for encapsulating a component's DOM subtree.

Example: A custom element can isolate some internal markup and styles.

Signing in once to access multiple connected applications.

Example: Staff authenticate through one identity provider for several tools.

A web app that updates its interface without full page navigation for many actions.

Example: A mail client switches folders without reloading the whole document.

Service Level Agreement, a formal commitment about service expectations.

Example: A contract may guarantee defined uptime targets.

Service Level Indicator, a measured reliability characteristic.

Example: The percentage of successful requests is an SLI.

Service Level Objective, a target for service reliability.

Example: A service may target successful responses for 99.9% of requests.

A place in a shadow tree where a component's external content is displayed.

Example: A card component exposes a slot for its title.

Simple Mail Transfer Protocol: commonly used to transmit outgoing email between servers.

Example: An email server sends a message to another mail server via SMTP.

A server that accepts and forwards email toward another mail system.

Example: An organization sends outbound mail through an SMTP relay.

A recorded point-in-time state of data or a virtual resource.

Example: An operator takes a volume snapshot before an upgrade.

Server Name Indication, a TLS extension carrying the intended hostname during handshake setup.

Example: Shared hosting uses SNI to select a site's certificate.

Start of Authority record containing administrative information about a DNS zone.

Example: A zone's SOA includes serial and timing fields.

A software endpoint used to send or receive data over a network.

Example: A browser opens a socket as part of a network connection.

A page that appears missing or empty despite returning a success HTTP status.

Example: An unavailable product page says not found but responds with 200.

Applications delivered to users over a network as an ongoing service.

Example: A browser-based project management app is SaaS.

A file mapping transformed code back to original sources for debugging.

Example: Browser developer tools use source maps to display original code.

Single-Page Application: an app that updates its interface without full document navigation for many actions.

Example: A dashboard can switch views without a full page reload.

An individual timed operation within a distributed trace.

Example: A span measures one database query during a request.

A targeted phishing attempt tailored to a particular person or organization.

Example: An attacker impersonates a known vendor in a personalized email.

Sender Policy Framework: a DNS-based mechanism advertising permitted sending hosts for a domain.

Example: A receiving server can evaluate an email's SPF result.

A DMARC check relating the authenticated SPF domain to the visible From domain.

Example: An email can pass SPF but fail DMARC alignment.

Providing different DNS answers according to the querying client or network.

Example: Internal staff can resolve a private host address not shown publicly.

Manipulating database queries by placing untrusted input into SQL code.

Example: Parameterized queries help prevent malicious query structure.

A DNS record advertising the host and port for a named service.

Example: Some messaging protocols discover service endpoints via SRV.

Static Site Generation: producing HTML pages ahead of requests.

Example: A documentation website can be built into static HTML files.

A DNS record containing fingerprints of a host's SSH keys.

Example: An SSH client may check SSHFP records when supported.

Service Set Identifier, the advertised name of a Wi-Fi network.

Example: A guest network may have a distinct SSID.

Secure Sockets Layer: the obsolete predecessor to TLS; often used informally to mean TLS.

Example: A so-called SSL certificate is generally used with modern TLS.

Server-Side Rendering: generating page HTML on a server for initial delivery.

Example: A server can pre-render product details for the browser.

Server-Side Request Forgery, where a server is induced to make unintended network requests.

Example: An unsafe URL fetcher may access internal-only services.

A pre-production environment for testing changes before release.

Example: A team can review a redesigned page on staging.

A caching directive allowing stale content to be served while refreshing it in the background.

Example: A cache quickly serves an older article while requesting a fresh copy.

An organization coordinating and publishing technical specifications.

Example: A standards body convenes contributors to refine interoperability rules.

A protocol command upgrading a plaintext connection to TLS when supported.

Example: An SMTP client can negotiate STARTTLS before sending credentials.

A firewall that tracks the state of network connections when filtering traffic.

Example: Return traffic is allowed for a permitted outgoing connection.

A tool that builds ready-to-serve HTML pages from templates and content.

Example: A documentation website generates HTML during its build.

An HTTP response field instructing browsers to prefer HTTPS for a host.

Example: HSTS helps prevent accidental HTTP connections after policy is learned.

Machine-readable annotations describing entities and relationships on a page.

Example: Product markup can specify price and availability when accurate.

A domain name placed under a parent domain.

Example: support.example.org can host a separate help center.

A logical subdivision of an IP network.

Example: An office might divide devices into different subnets.

A DNS record for publishing service endpoint connection parameters.

Example: A service can use SVCB to identify alternative endpoints.

Scalable Vector Graphics, an XML-based vector image format supported by browsers.

Example: A website displays a sharp logo with inline SVG.

A network device that forwards frames within a local network.

Example: An office switch connects computers and printers.

Encryption using the same secret key for encrypting and decrypting data.

Example: A TLS session can protect traffic using symmetric encryption.

A TCP flag used to begin synchronizing sequence numbers during connection setup.

Example: A TCP connection starts with a SYN segment.

Transmission Control Protocol, a reliable ordered transport protocol.

Example: A browser can establish a TCP connection before using HTTP/1.1.

The initial exchange that establishes a TCP connection.

Example: A client sends SYN, receives SYN-ACK, and sends ACK.

An infrastructure-as-code tool for provisioning resources through providers.

Example: A team uses Terraform to create test environments.

Content offering little original or useful information relative to its purpose.

Example: A near-empty product page may not answer buyers' questions.

Systematically identifying potential threats and security controls for a system.

Example: Developers model abuse cases before releasing a payment feature.

The actual rate of useful data transferred over a connection.

Example: Congestion may reduce throughput below the advertised link speed.

The delay between a request beginning and the first response byte arriving.

Example: Slow backend processing can raise TTFB.

A short-lived authentication code generated from a shared secret and current time.

Example: An authenticator app displays a rotating six-digit code.

The HTML head element setting a document's title.

Example: A unique title appears in the browser tab and can inform search results.

Transport Layer Security: a protocol for securing communications against eavesdropping and tampering.

Example: HTTPS relies on TLS to protect data in transit.

A modern TLS protocol version with streamlined secure handshakes.

Example: A current browser may establish an HTTPS connection with TLS 1.3.

The negotiation that authenticates a server and establishes encryption keys.

Example: An HTTPS client validates a certificate during the TLS handshake.

A DNS record associating a TLS service with certificate or key information.

Example: DANE deployments publish TLSA records for mail transport.

The last label of a domain name, such as .org or .com.

Example: In example.org, .org is the TLD.

A lab metric estimating main-thread blocking time during page loading.

Example: Long JavaScript tasks can increase TBT.

A diagnostic tool that probes the path packets take through networks.

Example: Traceroute can reveal intermediate network hops.

Deliberately controlling the rate or timing of network traffic.

Example: A router smooths bursts of backup traffic with traffic shaping.

An HTTP/1.1 field describing message-body transfer codings.

Example: Chunked transfer coding sends a body in successive chunks.

A service in which one network pays another for connectivity to other networks.

Example: A small ISP may purchase upstream IP transit.

A tool converting source code from one language version or syntax to another.

Example: A transpiler converts newer JavaScript syntax for selected environments.

A build optimization that removes unused code from bundles.

Example: An unused exported function may be excluded from production output.

Time to First Byte: the elapsed time before the first response byte arrives.

Example: Slow application logic can increase TTFB.

Time to Live: how long a cache may reuse data before refreshing it.

Example: A DNS record with TTL 300 is commonly cacheable for five minutes.

Encapsulating one protocol within another to transport it across a network.

Example: An IPv6 tunnel can carry packets across an IPv4-only section.

Metadata that can influence link previews on X and compatible platforms.

Example: A summary_large_image card can display a wide preview picture.

A DNS record containing text often used for verification and mail policies.

Example: A TXT record can publish SPF policy information.

User Datagram Protocol, a connectionless transport protocol without built-in delivery guarantees.

Example: Live voice traffic can be carried over UDP.

Communication from one sender to one specific destination.

Example: A browser usually sends a unicast request to a web server.

The organization maintaining the Unicode Standard for text characters.

Example: Unicode assigns code points used in multilingual web content.

The proportion of time a service is available.

Example: 99.9% uptime is not the same as zero downtime.

Uniform Resource Identifier: a broader identifier that includes URLs and other resource identifiers.

Example: A URL is one kind of URI.

Uniform Resource Locator: an address describing where a resource is and how it can be accessed.

Example: https://example.com/docs/start identifies a web document.

How a person perceives and interacts with a product across tasks.

Example: Clear error messages improve a form's UX.

The controls and visual or textual surfaces through which people use a product.

Example: Buttons, menus, and dialogs are parts of a UI.

A request header that identifies client software, though it can be modified or reduced.

Example: Servers may use User-Agent for compatibility handling.

An HTTP response field identifying request fields influencing the representation.

Example: Vary: Accept-Encoding separates compressed variants in caches.

Increasing the power of an existing machine or instance.

Example: Upgrading CPU and RAM is vertical scaling.

The area of a page currently available for viewing in a browser.

Example: Responsive layouts react to viewport size.

A software-defined computer running an operating system in a virtualized environment.

Example: A VM can host a Linux web server.

Virtual Local Area Network, a logical division of an Ethernet network.

Example: A company can place guest devices on a separate VLAN.

Voice over Internet Protocol: carrying voice communications over IP networks.

Example: An internet phone call is an example of VoIP.

Virtual Private Network: a tunnel connecting devices or networks over another network.

Example: A company VPN can provide access to internal resources.

World Wide Web Consortium, an organization producing web standards and accessibility guidance.

Example: The W3C publishes WCAG accessibility recommendations.

Web Application Firewall, filtering HTTP traffic according to configured rules.

Example: A WAF blocks requests matching known attack patterns.

A JSON file describing installable web-app identity and display settings.

Example: A PWA manifest specifies its name and icons.

A reusable browser-based component often built using custom elements and Shadow DOM.

Example: A custom date picker can be packaged as a web component.

A JSON file describing installable web app metadata and behavior.

Example: A manifest can specify app name, icons, and display mode.

A document or application view presented by a browser, usually identified by a URL.

Example: A product page and a checkout page can belong to one website.

Software or hardware that responds to requests for web resources.

Example: A server can return HTML for a requested page.

The browser APIs exposing localStorage and sessionStorage.

Example: A simple widget stores settings using Web Storage.

A browser script executing in a background thread apart from the page's main thread.

Example: A worker processes large datasets without blocking typing.

A portable binary instruction format used to run compiled code in supported runtimes.

Example: An image editor can perform compute-heavy work using WebAssembly.

A browser API for registering and using public-key authentication credentials.

Example: A website authenticates a user with a passkey through WebAuthn.

A browser API for hardware-accelerated 2D and 3D graphics.

Example: A web viewer rotates a 3D model using WebGL.

A modern browser API for GPU computation and graphics.

Example: A visualization app runs rendering calculations with WebGPU.

An HTTP callback sent when an event occurs in another system.

Example: A payment platform can notify a shop when an order is paid.

Web Real-Time Communication: browser APIs and protocols used for real-time media and data exchange.

Example: A video call can use WebRTC for audio and video.

A collection of related web pages and resources typically published under a common domain.

Example: A news website may contain articles, search pages, and account settings.

A protocol supporting ongoing two-way messaging over one connection.

Example: A collaborative app can send live changes over WebSockets.

A web API and transport mechanism for bidirectional communication over HTTP/3.

Example: A real-time app can exchange datagrams and streams using WebTransport.

Web Hypertext Application Technology Working Group, which maintains the HTML Living Standard and related standards.

Example: Browser developers follow WHATWG HTML specifications.

A protocol and label historically used to query registration information for internet resources.

Example: A WHOIS lookup may reveal limited domain registration details.

Wireless local networking based on the IEEE 802.11 family of standards.

Example: A phone uses Wi-Fi to reach its home router.

A DNS record that can match otherwise nonexistent names under a domain.

Example: A wildcard can direct many subdomains to the same host.

The system of linked resources accessed through web browsers using web addresses and web protocols.

Example: The web is one service on the internet; email is another.

A modern Wi-Fi security standard for protecting wireless network access.

Example: A WPA3-Personal network uses SAE for password-based authentication.

A security response header that discourages MIME-type sniffing.

Example: A site can send nosniff to enforce declared types.

Extensible Markup Language: a markup format for structured data.

Example: An RSS feed is often represented in XML.

A file listing important URLs and optional metadata to aid discovery.

Example: A sitemap can list a site's documentation pages.

Cross-Site Scripting: injecting untrusted content that executes as script in another user's page.

Example: Unsafe rendering of a comment can enable XSS.

An approach that grants application access based on verified identity and context.

Example: An employee accesses one internal app without joining the entire network.

A DNS mechanism that replicates zone records between servers.

Example: Secondary authoritative servers may use AXFR to synchronize a zone.