SEO glossary

A 301 redirect is an HTTP response telling browsers and search engines that a URL has moved permanently to a new address.

A 302 redirect is an HTTP response that sends users to another URL temporarily, signaling that the original address should stay in search results.

Answer engine optimization (AEO) is structuring content so search engines, voice assistants and AI chatbots can use it as the direct answer to a question.

An AI crawler is a bot run by an AI company that fetches web pages to train models, build an AI search index or answer a user’s request in real time.

AI Overviews are AI-generated summaries that Google shows at the top of some search results, with links to the web pages used as sources.

Alt text is the text in an image’s alt attribute that describes it for screen readers, search engines and anyone whose browser can’t load the image.

Anchor text is the visible, clickable text of a hyperlink; search engines use it to understand what the linked page is about.

A backlink is a link from another website to yours; search engines treat relevant backlinks as signals of trust and use them to discover pages.

A breadcrumb is a trail of links, such as Home › Guides › Boots, that shows where a page sits in a site’s hierarchy and lets users move up a level.

A broken link is a hyperlink whose target no longer loads, returning an error such as 404, 410 or 5xx, or failing at DNS or connection level.

A canonical tag (rel="canonical") tells search engines which URL is the preferred version of a page when the same content is reachable at several URLs.

Cumulative Layout Shift (CLS) measures how much visible content unexpectedly moves while a page is open; a good score is 0.1 or less.

A CMS (content management system) is software that lets people create, edit and publish website content without writing code for each page.

Core Web Vitals are Google’s three user-experience metrics — LCP for loading, INP for responsiveness and CLS for visual stability — measured on real users.

Crawl budget is the number of URLs a search engine is able and willing to crawl on a site in a given time, set by server capacity and crawl demand.

Click-through rate (CTR) is the percentage of impressions that turn into clicks: clicks divided by impressions, multiplied by 100.

DNS (Domain Name System) is the internet’s directory that translates domain names like example.com into the IP addresses of the servers that host them.

Domain age is the time since a domain name was first registered, as recorded in the registry’s RDAP or WHOIS data.

Domain Authority is a 1–100 score from Moz that predicts how well a site might rank based on its links; it is a third-party metric that Google doesn’t use.

Duplicate content is identical or substantially similar content that is reachable at more than one URL, on the same site or across different sites.

E-E-A-T (Experience, Expertise, Authoritativeness, Trustworthiness) is Google’s framework for judging whether content and its creators are credible.

A featured snippet is a highlighted excerpt Google extracts from one web page and shows prominently in results to answer a query directly.

Generative engine optimization (GEO) is the practice of making content accessible, understandable and citable for AI systems that generate answers.

Google Search Console is a free Google service that shows how a site performs in Google Search and reports indexing, crawling and other issues.

Google-Extended is a robots.txt product token that lets sites opt out of their content being used to train and ground Google’s Gemini models.

GPTBot is OpenAI’s web crawler that collects publicly available pages that may be used to train its generative AI models.

Hreflang is an HTML or HTTP annotation that tells search engines which language and regional versions of a page exist, so each user gets the right one.

HSTS is an HTTP response header that tells browsers to connect to a site only over HTTPS for a set period, blocking downgrade attacks.

HTTPS is HTTP sent over an encrypted TLS connection, which protects data in transit and proves to browsers that they reached the genuine site.

Indexing is the process in which a search engine analyzes a crawled page and stores it in its index, making it eligible to appear in search results.

IndexNow is an open protocol that lets websites instantly notify participating search engines when URLs are added, updated or deleted.

Interaction to Next Paint (INP) measures how quickly a page visibly responds to clicks, taps and key presses; good is 200 milliseconds or less.

Internal linking means linking pages within the same website, helping users navigate and search engines discover, understand and prioritize pages.

JavaScript SEO is the practice of making sure content and links generated by JavaScript can be crawled, rendered and indexed by search engines and AI bots.

JSON-LD (JavaScript Object Notation for Linked Data) is a W3C format for writing structured data as JSON inside a script tag; Google recommends it.

Keyword density is the number of times a word or phrase appears on a page divided by the page’s total word count, shown as a percentage.

Lazy loading delays loading images, iframes or other resources until they are about to scroll into view, saving bandwidth and speeding up the first load.

Largest Contentful Paint (LCP) measures how long the largest image or text block in the viewport takes to render; good is 2.5 seconds or less.

llms.txt is a proposed Markdown file at a site’s root that gives large language models a short summary and a curated list of the site’s key pages.

Local SEO is optimizing a business’s online presence so it appears in location-based searches, such as Google Maps and the local pack.

A long-tail keyword is a specific, lower-volume search query, often several words long, that expresses a precise need and usually faces less competition.

A meta description is an HTML meta tag that summarizes a page; search engines may show it as the snippet text under your title in results.

Mobile-first indexing means Google uses the smartphone version of a page, crawled by Googlebot Smartphone, for indexing and ranking.

Nofollow is a link attribute (rel="nofollow") telling search engines you don’t endorse the linked page and don’t want the link to pass ranking credit.

Noindex is a robots directive, set in a meta tag or HTTP header, that tells search engines not to include a page in their search results.

Off-page SEO is the work done outside your own website, such as earning backlinks, mentions and reviews, that builds its authority and reputation.

On-page SEO is optimizing the content and HTML of individual pages, such as titles, headings, text, images and links, to rank and earn clicks.

Open Graph is a set of meta tags (og:title, og:image and others) that define how a page appears when it’s shared on social networks and messaging apps.

An orphan page is a page on your site that no other internal page links to, so users and crawlers can only reach it through a sitemap or a direct URL.

Page speed describes how quickly a web page loads and becomes usable, measured with metrics such as TTFB, LCP and INP rather than one single number.

PageRank is Google’s original algorithm for scoring a page’s importance based on the number and quality of links pointing to it.

Pagination is splitting a long list of items, such as products or articles, across a sequence of numbered pages linked to one another.

A redirect chain is a sequence of two or more redirects between the requested URL and the final page that actually returns content.

Render-blocking resources are CSS and JavaScript files the browser must download and process before it can display any content on the page.

Rich results are search listings enhanced with extra visuals or data, such as review stars, prices, images or event dates, usually powered by structured data.

robots.txt is a plain-text file at the root of a site that tells crawlers which URL paths they may or may not fetch.

Schema markup is code that uses the schema.org vocabulary to label page content as specific entities, such as an Organization, Article, Product or Event.

Search intent is the underlying goal a person has when they type a query: to learn something, reach a site, compare options or complete an action.

Security headers are HTTP response headers that instruct browsers to enable protections against attacks such as XSS, clickjacking and protocol downgrades.

SEO (search engine optimization) is the practice of making web pages easy for search engines to crawl, understand and rank for relevant searches.

A SERP (search engine results page) is the page a search engine shows for a query: organic results, ads and features such as AI Overviews or maps.

A sitemap index is an XML file that lists other sitemap files, letting large sites split their URLs across several sitemaps and submit them as one.

An SSL certificate (properly, a TLS certificate) is a digital certificate that binds a domain name to a public key so browsers can set up HTTPS securely.

Structured data is standardized, machine-readable information added to a page’s code that describes what the content is, such as a product, recipe or event.

Technical SEO is optimizing a website’s infrastructure so search engines can crawl, render and index it efficiently and serve it fast and securely.

Thin content is a page with little or no original value for visitors, such as doorway pages, scraped text or near-empty templates.

The title tag is the HTML title element that names a page; Google uses it for the clickable title link in results and browsers show it in the tab.

Time to First Byte (TTFB) is the time between a browser requesting a page and receiving the first byte of the response from the server.

A Twitter Card is a set of twitter: meta tags that controls the preview, with title, description and image, shown when a link is posted on X (formerly Twitter).

A URL slug is the last, human-readable part of a URL path that identifies a specific page, such as waterproof-boots in /guides/waterproof-boots/.

A web crawler is an automated program that discovers and downloads web pages by following links, so search engines and AI systems can index them.

X-Robots-Tag is an HTTP response header that carries robots directives such as noindex or nosnippet, so they also work for PDFs, images and other files.

An XML sitemap is a file listing the URLs you want search engines to crawl and index, optionally with the date each page last changed.