ARIA (Accessible Rich Internet Applications)
A set of HTML attributes that define ways to make web content more accessible to people using assistive technologies.
Glossary
Quick definitions for common SEO, performance, and web terms.
Backlink
A hyperlink from one website pointing to a page on another website, used by search engines as a signal of authority and relevance.
Bounce Rate
The percentage of sessions in which a user leaves a site after viewing only one page, without interacting further.
CDN (Content Delivery Network)
How CDNs deliver static and cached content from edge locations to improve speed and reliability.
CLS (Cumulative Layout Shift)
A measure of how much unexpected layout shift occurs while a page loads.
CORS (Cross-Origin Resource Sharing)
A browser security mechanism that controls which cross-origin requests are permitted using HTTP response headers.
CSP (Content Security Policy)
A security header that controls which resources a page is allowed to load.
CSRF (Cross-Site Request Forgery)
An attack that tricks an authenticated user into unknowingly submitting requests to another site.
Canonical Tag
rel=canonical is used to indicate the preferred version of a page to search engines.
Clickjacking
An attack that overlays invisible iframes to trick users into clicking unintended targets.
Compression (Brotli / Gzip)
Server-side encoding that reduces text-based file transfer sizes for faster page loads.
Core Web Vitals
A set of performance metrics (Largest Contentful Paint, Interaction to Next Paint, Cumulative Layout Shift) that measure user experience.
Crawl Budget
The number of pages a search engine will crawl on your site within a given timeframe.
DKIM (DomainKeys Identified Mail)
An email authentication method that uses digital signatures to verify message integrity.
DMARC
A policy that tells receiving mail servers what to do when SPF or DKIM checks fail.
DNS
The Domain Name System maps human-readable domain names to IP addresses and other records.
DNS A Record
Maps a hostname to an IPv4 address.
DNS AAAA Record
Maps a hostname to an IPv6 address.
DNS CAA Record
Specifies which certificate authorities are allowed to issue SSL/TLS certificates for a domain.
DNS CNAME Record
Aliases one hostname to another hostname.
DNS MX Record
Specifies mail servers responsible for receiving email.
DNS NS Record
Specifies the authoritative nameservers for a domain.
DNS TXT Record
Stores arbitrary text data for a domain, often for verification.
DNSSEC
DNS Security Extensions provide a way to verify DNS data integrity and authenticity.
E-E-A-T
Google's quality framework: Experience, Expertise, Authoritativeness, Trustworthiness.
FCP (First Contentful Paint)
The time until the first text or image is painted on the screen.
FID (First Input Delay)
A legacy responsiveness metric measuring delay before the browser handles user input.
HSTS (HTTP Strict Transport Security)
A security policy that forces browsers to only access a site over HTTPS.
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, introducing multiplexing and header compression for faster connections.
HTTP/3
The third major version of HTTP, built on QUIC for faster and more resilient connections.
HTTPS
How HTTPS encrypts web traffic using TLS to protect data in transit.
INP (Interaction to Next Paint)
A responsiveness metric measuring how quickly a page responds to user input.
Keyword (SEO)
A word or phrase that people use to find content in search engines.
LCP (Largest Contentful Paint)
The time it takes for the largest above-the-fold element to render.
Lab Data
Performance data measured in a controlled environment.
Lazy Loading
A technique that defers loading of non-critical resources (images, scripts, iframes) until they are needed, typically when they scroll into view.
Lighthouse
Google\
Meta Description
An HTML tag summarising a page content, shown as the snippet in search engine results.
Mobile-First Indexing
Google\
Open Graph
Meta tags that control how pages appear when shared on social media.
Permissions Policy
An HTTP response header that lets a site control which browser features and APIs can be used in the page and in embedded iframes.
RUM (Real User Monitoring)
Performance data collected from real users in production.
Redirect (301 / 302)
How HTTP redirects work and when to use 301 (permanent) vs 302 (temporary).
Referrer Policy
An HTTP header and HTML meta attribute that controls how much referrer information is included in requests when a user navigates from your site.
SPF (Sender Policy Framework)
A DNS record that specifies which mail servers are authorised to send email for a domain.
SQL Injection
An attack where malicious SQL code is inserted into queries via user input.
SSL/TLS
The cryptographic protocols that secure data transmitted over the internet.
Structured Data (Schema.org)
Using Schema.org and JSON-LD to add machine-readable context to your pages.
TBT (Total Blocking Time)
A lab metric estimating how much the main thread is blocked during load.
TTFB (Time To First Byte)
The time it takes for the first byte of a server response to reach the browser.
TTL (Time To Live)
A DNS record property indicating how long a resolver may cache that record.
URL
What a URL is and its parts (protocol, domain, path, parameters).
Uptime Monitoring
The practice of automatically checking whether a website or service is reachable and responding correctly, typically at regular intervals.
WCAG (Web Content Accessibility Guidelines)
A simple guide to WCAG and the four POUR principles.
XSS (Cross‑Site Scripting)
A web security vulnerability where attackers inject malicious scripts into webpages.
hreflang
How to use hreflang annotations to target content by language and region.
llms.txt / ai.txt
Site guidance files for LLMs and AI crawlers — how you want your content to be used.
noindex
A directive that prevents a page from appearing in search engine results.
robots.txt
Small text file that tells crawlers which parts of a site to crawl or avoid.
sitemap.xml
What a sitemap is and how it helps crawlers discover your important URLs.