ARIA (Accessible Rich Internet Applications)
A W3C specification of HTML attributes that expose roles, states, and properties of UI components to assistive technology.
Glossary
Quick definitions for common SEO, performance, and web terms.
Backlink
A hyperlink from one website to another, used by search engines as a signal of authority and relevance.
Bounce Rate
A legacy Universal Analytics metric for single-page sessions, replaced by engagement rate in Google Analytics 4.
CDN (Content Delivery Network)
A network of edge servers that caches content close to users to reduce latency and origin load.
CLS (Cumulative Layout Shift)
A Core Web Vitals metric that measures unexpected layout shifts during a page load.
CORS (Cross-Origin Resource Sharing)
A browser mechanism that uses HTTP headers to control which cross-origin requests are allowed.
CSP (Content Security Policy)
A response header that tells the browser which content sources a page is allowed to load and execute.
CSRF (Cross-Site Request Forgery)
An attack that tricks an authenticated browser into submitting unwanted requests to another site.
Canonical Tag
A `rel="canonical"` link element that tells search engines the preferred URL when the same content is reachable from several addresses.
Clickjacking
A UI redress attack that overlays your site invisibly on a malicious page to trick users into unintended clicks.
Compression (Brotli / Gzip)
Server-side encoding that shrinks text-based responses before transit, cutting bandwidth and improving page load.
Core Web Vitals
Google's set of user-experience metrics: LCP for loading, INP for responsiveness, and CLS for visual stability.
Crawl Budget
The number of URLs a search engine will crawl on your site within a given timeframe.
DKIM (DomainKeys Identified Mail)
An email authentication standard that uses a DNS-published public key to verify message signatures.
DMARC
A policy record telling receiving mail servers what to do when SPF or DKIM checks fail.
DNS
The Domain Name System resolves human-readable names like example.com to IP addresses and other records that drive web, email, and security.
DNS A Record
A DNS record that maps a hostname like www.example.com to a single IPv4 address so clients know where to send traffic.
DNS AAAA Record
A DNS record that maps a hostname to an IPv6 address, the IPv6 counterpart of an A record used for dual-stack reachability.
DNS CAA Record
A DNS record that controls which certificate authorities are allowed to issue TLS certificates for a domain.
DNS CNAME Record
A DNS record that aliases one hostname to another so the target hostname resolves and inherits its A and AAAA records.
DNS MX Record
A DNS record that lists the mail servers responsible for receiving email for a domain, each with a priority value.
DNS NS Record
A DNS record that names the authoritative nameservers responsible for answering queries about a domain.
DNS TXT Record
A DNS record that stores arbitrary text for a domain, used for verification, ownership proofs, and email authentication.
DNSSEC
DNS Security Extensions add cryptographic signatures to DNS records so resolvers can verify responses are authentic and unmodified.
E-E-A-T
Google's quality framework: Experience, Expertise, Authoritativeness, Trustworthiness, used by quality raters to score pages.
FCP (First Contentful Paint)
The time from navigation until the browser paints the first text or image, signalling that loading has begun.
FID (First Input Delay)
A legacy Core Web Vital that measured the delay before the browser could process a user's first interaction.
HSTS (HTTP Strict Transport Security)
A response header that forces browsers to use HTTPS for all future requests to a domain.
HTTP Status Codes
Three-digit codes returned by a web server indicating whether an HTTP request succeeded, failed, or requires further action.
HTTP/2
The second major version of HTTP, adding multiplexing, header compression, and binary framing for faster connections.
HTTP/3
The third major version of HTTP, layered on the QUIC transport for lower latency and better resilience to packet loss.
HTTPS
The encrypted version of HTTP that uses TLS to protect data in transit between browser and server.
INP (Interaction to Next Paint)
A Core Web Vitals metric that measures how quickly a page responds to user interactions.
Keyword (SEO)
A word or phrase users type into search engines to find content, used to target and structure pages for SEO.
LCP (Largest Contentful Paint)
A Core Web Vital measuring the render time of the largest visible element in the viewport.
Lab Data
Performance measurements taken in a controlled environment with fixed device and network settings, used for repeatable testing.
Lazy Loading
A technique that defers loading of non-critical resources like images, iframes, and scripts until they are needed.
Lighthouse
Google's open-source auditing tool that scores pages on performance, accessibility, SEO, and best practices.
Meta Description
An HTML tag summarising a page's content, often shown as the snippet in search results.
Mobile-First Indexing
Google's practice of using the mobile version of a site as the primary source for indexing and ranking.
Open Graph
Meta tags that control how a page appears when shared on social platforms.
Permissions Policy
An HTTP response header that controls which browser features and APIs can run on a page and in its embedded frames.
RUM (Real User Monitoring)
Performance data collected from real visitors in production, reflecting their actual devices, networks, and behaviour.
Redirect (301 / 302)
How HTTP redirects work and when to use 301 (permanent) versus 302 (temporary).
Referrer Policy
An HTTP header and HTML attribute that controls how much referrer URL information is sent on outgoing requests.
SPF (Sender Policy Framework)
A DNS TXT record that lists the mail servers authorised to send email for a domain.
SQL Injection
A web vulnerability where untrusted input is concatenated into SQL queries, letting an attacker run arbitrary database commands.
SSL/TLS
The cryptographic protocols that authenticate servers and encrypt traffic between clients and servers on the web.
Structured Data (Schema.org)
Machine-readable markup, usually JSON-LD, that describes page content using the Schema.org vocabulary.
TBT (Total Blocking Time)
A lab metric that sums how long the main thread was blocked by long tasks between FCP and Time to Interactive.
TTFB (Time To First Byte)
The time between making a request and receiving the first byte of the response from the server.
TTL (Time To Live)
A DNS record value telling resolvers how long they may cache that record before refetching it.
URL
A Uniform Resource Locator: the structured address used to fetch a resource on the web, made of scheme, host, path, and optional query and fragment.
Uptime Monitoring
Automated checks that confirm a site is reachable and responding correctly, with alerts when it is not.
WCAG (Web Content Accessibility Guidelines)
The W3C standard for making web content accessible, organised around the four POUR principles and three conformance levels.
XSS (Cross‑Site Scripting)
A vulnerability where attackers inject scripts that run in another user's browser session.
hreflang
An HTML annotation that tells search engines which language and region each version of a page targets.
llms.txt / ai.txt
Plain-text files at the site root that publish how large language models and AI crawlers may use the content they fetch.
noindex
A directive that tells search engines to keep a page out of their index.
robots.txt
A plain-text file at the site root that tells crawlers which paths they may or may not request.
sitemap.xml
An XML file that lists important URLs on a site so search engines can discover and prioritize them.