# SEO glossary

> Plain-English definitions of SEO and AI-search terms — canonical, hreflang, Core Web Vitals, GEO, llms.txt and more — with examples and free checkers.

- [SEO](https://yes-seo.com/glossary/seo): SEO (search engine optimization) is the practice of making web pages easy for search engines to crawl, understand and rank for relevant searches.
- [SERP](https://yes-seo.com/glossary/serp): 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.
- [Title tag](https://yes-seo.com/glossary/title-tag): 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.
- [Meta description](https://yes-seo.com/glossary/meta-description): 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.
- [Canonical tag](https://yes-seo.com/glossary/canonical-tag): 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.
- [robots.txt](https://yes-seo.com/glossary/robots-txt): 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.
- [XML sitemap](https://yes-seo.com/glossary/xml-sitemap): 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.
- [Sitemap index](https://yes-seo.com/glossary/sitemap-index): 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.
- [Noindex](https://yes-seo.com/glossary/noindex): 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.
- [Nofollow](https://yes-seo.com/glossary/nofollow): 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.
- [X-Robots-Tag](https://yes-seo.com/glossary/x-robots-tag): 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.
- [Hreflang](https://yes-seo.com/glossary/hreflang): 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.
- [Structured data](https://yes-seo.com/glossary/structured-data): 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.
- [Schema markup](https://yes-seo.com/glossary/schema-markup): 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.
- [JSON-LD](https://yes-seo.com/glossary/json-ld): 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.
- [Rich results](https://yes-seo.com/glossary/rich-results): 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.
- [Core Web Vitals](https://yes-seo.com/glossary/core-web-vitals): 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.
- [LCP (Largest Contentful Paint)](https://yes-seo.com/glossary/lcp): 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.
- [INP (Interaction to Next Paint)](https://yes-seo.com/glossary/inp): Interaction to Next Paint (INP) measures how quickly a page visibly responds to clicks, taps and key presses; good is 200 milliseconds or less.
- [CLS (Cumulative Layout Shift)](https://yes-seo.com/glossary/cls): Cumulative Layout Shift (CLS) measures how much visible content unexpectedly moves while a page is open; a good score is 0.1 or less.
- [TTFB (Time to First Byte)](https://yes-seo.com/glossary/ttfb): 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.
- [Page speed](https://yes-seo.com/glossary/page-speed): 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.
- [Render-blocking resources](https://yes-seo.com/glossary/render-blocking): Render-blocking resources are CSS and JavaScript files the browser must download and process before it can display any content on the page.
- [Lazy loading](https://yes-seo.com/glossary/lazy-loading): 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.
- [Web crawler](https://yes-seo.com/glossary/crawler): 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.
- [Crawl budget](https://yes-seo.com/glossary/crawl-budget): 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.
- [Indexing](https://yes-seo.com/glossary/indexing): 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.
- [Mobile-first indexing](https://yes-seo.com/glossary/mobile-first-indexing): Mobile-first indexing means Google uses the smartphone version of a page, crawled by Googlebot Smartphone, for indexing and ranking.
- [JavaScript SEO](https://yes-seo.com/glossary/javascript-seo): 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.
- [Backlink](https://yes-seo.com/glossary/backlink): 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.
- [Anchor text](https://yes-seo.com/glossary/anchor-text): Anchor text is the visible, clickable text of a hyperlink; search engines use it to understand what the linked page is about.
- [Internal linking](https://yes-seo.com/glossary/internal-linking): Internal linking means linking pages within the same website, helping users navigate and search engines discover, understand and prioritize pages.
- [Orphan page](https://yes-seo.com/glossary/orphan-page): 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.
- [PageRank](https://yes-seo.com/glossary/pagerank): PageRank is Google’s original algorithm for scoring a page’s importance based on the number and quality of links pointing to it.
- [Domain authority](https://yes-seo.com/glossary/domain-authority): 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.
- [301 redirect](https://yes-seo.com/glossary/redirect-301): A 301 redirect is an HTTP response telling browsers and search engines that a URL has moved permanently to a new address.
- [302 redirect](https://yes-seo.com/glossary/redirect-302): A 302 redirect is an HTTP response that sends users to another URL temporarily, signaling that the original address should stay in search results.
- [Redirect chain](https://yes-seo.com/glossary/redirect-chain): A redirect chain is a sequence of two or more redirects between the requested URL and the final page that actually returns content.
- [Broken link](https://yes-seo.com/glossary/broken-link): 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.
- [Alt text](https://yes-seo.com/glossary/alt-text): 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.
- [Keyword density](https://yes-seo.com/glossary/keyword-density): 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.
- [Long-tail keyword](https://yes-seo.com/glossary/long-tail-keyword): 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.
- [Search intent](https://yes-seo.com/glossary/search-intent): 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.
- [E-E-A-T](https://yes-seo.com/glossary/eeat): E-E-A-T (Experience, Expertise, Authoritativeness, Trustworthiness) is Google’s framework for judging whether content and its creators are credible.
- [Duplicate content](https://yes-seo.com/glossary/duplicate-content): Duplicate content is identical or substantially similar content that is reachable at more than one URL, on the same site or across different sites.
- [Thin content](https://yes-seo.com/glossary/thin-content): Thin content is a page with little or no original value for visitors, such as doorway pages, scraped text or near-empty templates.
- [Featured snippet](https://yes-seo.com/glossary/featured-snippet): A featured snippet is a highlighted excerpt Google extracts from one web page and shows prominently in results to answer a query directly.
- [CTR (click-through rate)](https://yes-seo.com/glossary/ctr): Click-through rate (CTR) is the percentage of impressions that turn into clicks: clicks divided by impressions, multiplied by 100.
- [AI Overviews](https://yes-seo.com/glossary/ai-overviews): 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.
- [GEO (generative engine optimization)](https://yes-seo.com/glossary/generative-engine-optimization): Generative engine optimization (GEO) is the practice of making content accessible, understandable and citable for AI systems that generate answers.
- [AEO (answer engine optimization)](https://yes-seo.com/glossary/answer-engine-optimization): 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.
- [llms.txt](https://yes-seo.com/glossary/llms-txt): 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.
- [AI crawler](https://yes-seo.com/glossary/ai-crawler): 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.
- [GPTBot](https://yes-seo.com/glossary/gptbot): GPTBot is OpenAI’s web crawler that collects publicly available pages that may be used to train its generative AI models.
- [Google-Extended](https://yes-seo.com/glossary/google-extended): 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.
- [IndexNow](https://yes-seo.com/glossary/indexnow): IndexNow is an open protocol that lets websites instantly notify participating search engines when URLs are added, updated or deleted.
- [Google Search Console](https://yes-seo.com/glossary/google-search-console): Google Search Console is a free Google service that shows how a site performs in Google Search and reports indexing, crawling and other issues.
- [HTTPS](https://yes-seo.com/glossary/https): HTTPS is HTTP sent over an encrypted TLS connection, which protects data in transit and proves to browsers that they reached the genuine site.
- [SSL certificate](https://yes-seo.com/glossary/ssl-certificate): 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.
- [HSTS (HTTP Strict Transport Security)](https://yes-seo.com/glossary/hsts): HSTS is an HTTP response header that tells browsers to connect to a site only over HTTPS for a set period, blocking downgrade attacks.
- [Security headers](https://yes-seo.com/glossary/security-headers): Security headers are HTTP response headers that instruct browsers to enable protections against attacks such as XSS, clickjacking and protocol downgrades.
- [Open Graph](https://yes-seo.com/glossary/open-graph): 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.
- [Twitter Card](https://yes-seo.com/glossary/twitter-card): 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).
- [Breadcrumb](https://yes-seo.com/glossary/breadcrumb): 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.
- [URL slug](https://yes-seo.com/glossary/url-slug): 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/.
- [Pagination](https://yes-seo.com/glossary/pagination): Pagination is splitting a long list of items, such as products or articles, across a sequence of numbered pages linked to one another.
- [On-page SEO](https://yes-seo.com/glossary/on-page-seo): 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.
- [Off-page SEO](https://yes-seo.com/glossary/off-page-seo): Off-page SEO is the work done outside your own website, such as earning backlinks, mentions and reviews, that builds its authority and reputation.
- [Technical SEO](https://yes-seo.com/glossary/technical-seo): Technical SEO is optimizing a website’s infrastructure so search engines can crawl, render and index it efficiently and serve it fast and securely.
- [Local SEO](https://yes-seo.com/glossary/local-seo): Local SEO is optimizing a business’s online presence so it appears in location-based searches, such as Google Maps and the local pack.
- [DNS (Domain Name System)](https://yes-seo.com/glossary/dns): 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](https://yes-seo.com/glossary/domain-age): Domain age is the time since a domain name was first registered, as recorded in the registry’s RDAP or WHOIS data.
- [CMS (content management system)](https://yes-seo.com/glossary/cms): A CMS (content management system) is software that lets people create, edit and publish website content without writing code for each page.