---
title: "SEO glossary: every term defined"
slug: "glossary"
category: "seo"
tags: ["seo", "glossary", "definitions", "reference", "terminology", "search"]
status: "stable"
last_updated: 2026-08-14
summary: "Comprehensive SEO glossary: every term a developer or content editor needs, grouped by category and linked to the deep-dive page for each concept."
faqPage: true
related: ["[[seo/technical]]", "[[seo/content]]", "[[seo/structured-data]]", "[[seo/ai-search-optimization]]", "[[seo/discoverability-files]]", "[[seo/helpful-content-update]]", "[[seo/e-e-a-t]]"]
---
## Overview
SEO has its own vocabulary that crosses search engines, content strategy, structured data, performance, and AI search. This page defines every term once, links to the deep-dive where one exists, and groups terms by category so a developer or editor can navigate by domain. Use this as the citation anchor for every other SEO page in the vault.
## Table of contents
- [Core search concepts](#core-search-concepts)
- [Crawling and indexing](#crawling-and-indexing)
- [On-page SEO](#on-page-seo)
- [Off-page SEO](#off-page-seo)
- [Technical SEO](#technical-seo)
- [Structured data](#structured-data)
- [Performance and Core Web Vitals](#performance-and-core-web-vitals)
- [AI search and agent readability](#ai-search-and-agent-readability)
- [Content strategy](#content-strategy)
- [Discoverability files](#discoverability-files)
- [SERP features](#serp-features)
- [Penalties and recovery](#penalties-and-recovery)
- [Local SEO](#local-seo)
- [Analytics and tooling](#analytics-and-tooling)
## Core search concepts
### What is SEO (Search Engine Optimization)?
SEO (Search Engine Optimization) is the practice of improving a site's organic visibility in search engines. Covers technical setup, content quality, structured data, and external signals. The umbrella term for everything on this site. See [[seo/technical]] for the technical baseline and [[seo/content]] for the content layer.
### What is a SERP (Search Engine Result Page)?
A SERP (Search Engine Result Page) is the page returned by a search engine for a given query. Contains organic results, ads, and SERP features (featured snippets, People Also Ask, knowledge panels). See [[seo/serp-features]].
### What is a search engine?
A search engine is a system that crawls, indexes, and ranks web pages. The big four are Google, Bing, Baidu, and Yandex. AI search engines (ChatGPT search, Perplexity, Claude, Google AI Overviews) are a growing fifth category. See [[seo/ai-search-optimization]].
### What is search intent?
Search intent is what the searcher actually wants when they type a query. The four classic categories are informational, navigational, commercial, and transactional. Matching intent is the single highest-impact content rule. See [[seo/content]].
### What is a query?
A query is the string a user types or speaks into a search engine. The unit ranking systems compete on.
### What is ranking?
Ranking is the position a page holds in the SERP for a given query. Affected by hundreds of signals, but driven by topical authority, technical health, and user-engagement metrics.
### What is organic traffic?
Organic traffic is visits from unpaid search results. Distinct from paid (ads), direct (URL typed), referral (links), and social.
## Crawling and indexing
### What is a crawler?
A crawler is a bot that fetches pages to discover content for indexing. Googlebot, Bingbot, and Applebot are the major commercial crawlers. AI engines run their own (GPTBot, ClaudeBot, PerplexityBot). See [[seo/javascript-seo]].
### What is crawl budget?
Crawl budget is the number of pages a search engine will fetch from a domain in a given period. Matters at scale (over 10k URLs). See [[seo/crawl-budget]].
### What is indexing?
Indexing is the process of parsing a fetched page and storing its content in the search engine's database. Indexed pages can rank; non-indexed pages cannot.
### What is index coverage?
Index coverage is a Google Search Console report showing which pages are indexed, excluded, or erroring. The first place to check when traffic drops. See [[howto/master-google-search-console]].
### What is noindex?
Noindex is a meta tag (``) or HTTP header that asks search engines to exclude the page from their index. The page can still be crawled and counted for link equity flow.
### What is nofollow?
Nofollow is a link attribute (`rel="nofollow"`) that tells search engines not to pass authority through the link. Used for paid, untrusted, or user-generated content.
### What are UGC and sponsored link attributes?
UGC and sponsored link attributes are two newer link-rel values: `rel="ugc"` for user-generated content (comments, forum posts) and `rel="sponsored"` for paid placements. More specific than `nofollow`.
### What is render budget?
Render budget is a sub-budget within crawl budget specifically for JavaScript execution. Googlebot defers JS-heavy pages to a second-pass renderer with delay. See [[seo/javascript-seo]].
### What is mobile-first indexing?
Mobile-first indexing is Google's policy of indexing the mobile version of a page rather than the desktop version. Active across all sites since 2021. See [[seo/mobile-first]].
## On-page SEO
### What is a title tag?
A title tag is the HTML `` element. The single highest-impact on-page lever. Google rewrites titles that are vague, stuffed, or mismatched to content. See [[seo/title-tags]].
### What is a meta description?
A meta description is the HTML `<meta name="description">` attribute. Not a ranking signal directly, but a CTR driver in the SERP snippet. See [[howto/write-meta-descriptions]].
### What is an H1?
An H1 is the single top-level heading on a page (`<h1>`). Should match the page intent and the title tag, but does not have to be identical.
### What are H2/H3?
H2/H3 are subheadings (`<h2>`, `<h3>`) for sections and sub-cases. Use them in order with no level skips. See [[seo/technical]].
### What is a slug?
A slug is the path component of a URL that identifies a page (`/seo/glossary` has slug `glossary`). Use short kebab-case noun phrases.
### What is a canonical URL?
A canonical URL is the one URL form chosen as the indexable version of a page. Declared with `<link rel="canonical">`. See [[glossary/canonical-url]] and [[seo/redirects]].
### What is anchor text?
Anchor text is the visible text of a hyperlink. Descriptive anchor text outperforms generic ("click here", "read more") for both SEO and accessibility. See [[seo/internal-linking]].
### What is keyword density?
Keyword density is the frequency of a target keyword in a page's body. Optimization on this metric specifically is obsolete; write naturally and the density falls out.
### What is keyword stuffing?
Keyword stuffing is cramming a target keyword into a page beyond natural usage. Triggers algorithmic downweighting. Avoid.
### What is a long-tail keyword?
A long-tail keyword is a multi-word, lower-volume query that is easier to rank for and converts better than head terms. The bread-and-butter of content strategy. See [[seo/keyword-research]].
### What is search intent classification?
Search intent classification is tagging each target keyword as informational, navigational, commercial, or transactional. Drives content format and depth.
### What is cannibalization?
Cannibalization is two pages on the same site competing for the same query, neither winning. See [[seo/cannibalization]].
## Off-page SEO
### What is a backlink?
A backlink is a link from another site pointing to yours. The original PageRank signal. Quality of referring domain matters more than count.
### What is an inbound link?
An inbound link is the same as a backlink: a link pointing into your site.
### What is an outbound link?
An outbound link is a link from your site pointing to another. Linking to authoritative sources is a trust signal.
### What is an internal link?
An internal link is a link from one page on your site to another page on your site. The strongest lever you control. See [[seo/internal-linking]].
### What is link equity?
Link equity is the ranking authority that flows through a link. Also called "link juice" historically.
### What is a referring domain?
A referring domain is a unique domain that links to your site. More valuable as a signal than total backlink count: ten links from ten domains beat 100 from one.
### What is disavow?
Disavow is a file submitted to Google Search Console listing toxic backlinks the site does not want associated. Use only after a manual action or clear algorithmic penalty.
### What is link building?
Link building is the practice of actively earning or acquiring backlinks. Modern best practice favors earning links through original research, reference content, and PR.
## Technical SEO
### What is robots.txt?
robots.txt is a file at the site root that declares crawl scope to bots. See [[seo/discoverability-files]].
### What is sitemap.xml?
sitemap.xml is an XML file at the site root listing every canonical URL with its `lastmod`. See [[seo/discoverability-files]].
### What is a 301 redirect?
A 301 redirect is a permanent redirect. Passes the bulk of link equity to the new URL. Default for all permanent URL changes. See [[seo/redirects]].
### What is a 302 redirect?
A 302 redirect is a temporary redirect. Does not pass full link equity. Used rarely (legitimate A/B tests, scheduled outages).
### What are 307 and 308 redirects?
307 and 308 redirects are HTTP/1.1 equivalents of 302 and 301 respectively, with the added guarantee that the request method (POST, GET) is preserved across the redirect.
### What is a soft 404?
A soft 404 is a 200 OK response on a page that has no real content (empty search results, missing product). Google detects these heuristically and excludes them. Return real 404s.
### What is hreflang?
Hreflang is a tag pair declaring language and region variants of a page. Required for multi-language and multi-region sites. See [[seo/hreflang]].
### What is canonicalization?
Canonicalization is the process of selecting one URL form as the indexable version. Self-referential canonicals on every indexable page prevent parameter and protocol drift.
### What are URL parameters?
URL parameters are query-string segments after `?`. SEO concern when parameters generate near-duplicate pages (sorting, filtering, tracking).
### What is faceted navigation?
Faceted navigation is filter UI (color, size, price) that generates parameterized URLs. Without crawl control, generates combinatorial explosion. See [[seo/pagination-and-facets]].
### What is pagination?
Pagination is splitting a long list into numbered pages. Modern best practice: self-canonical per page, no rel=prev/next. See [[seo/pagination-and-facets]].
### What is HSTS?
HSTS (HTTP Strict Transport Security) is a response header that forces browsers to use HTTPS for the domain. SEO-relevant because it prevents protocol-drift duplicate content.
## Structured data
### What is Schema.org?
Schema.org is the vocabulary used for structured data. A shared standard between Google, Bing, Yandex, and others.
### What is JSON-LD?
JSON-LD is the format Google recommends for embedding structured data. A `<script type="application/ld+json">` block in `<head>`. See [[seo/structured-data]].
### What is Microdata?
Microdata is an older inline format for structured data. Superseded by JSON-LD for most use cases.
### What is a rich result?
A rich result is a SERP listing enhanced by structured data (star ratings, FAQ accordions, recipe cards). See [[seo/schema-markup-deep]].
### What is Article schema?
Article schema is the JSON-LD type for editorial pages. Required: `headline`, `datePublished`, `dateModified`, `author`. See [[seo/e-e-a-t]].
### What is BreadcrumbList schema?
BreadcrumbList schema is JSON-LD declaring the page's position in the site hierarchy. Surfaces breadcrumb display in SERPs.
### What is FAQPage schema?
FAQPage schema is JSON-LD declaring a list of question-and-answer pairs. Google fully removed the FAQ rich result from Search in May 2026; the markup no longer earns an accordion snippet but is still valid schema.org and still aids page understanding and AI-agent parsing. See [[seo/schema-markup-deep]].
### What is HowTo schema?
HowTo schema is JSON-LD declaring step-by-step instructions. Google restricted HowTo rich results to desktop in August 2023 and removed them entirely the next month; the markup earns no SERP feature on any device but is still valid schema.org. See [[seo/schema-markup-deep]].
### What is Person schema?
Person schema is JSON-LD declaring an author entity. Pair with `sameAs` array linking to social and Wikidata. See [[seo/author-entities]].
### What is sameAs?
sameAs is a `Person` or `Organization` property listing public profile URLs (LinkedIn, GitHub, Wikipedia, Wikidata). The primary entity-resolution signal. See [[seo/author-entities]].
## Performance and Core Web Vitals
### What are Core Web Vitals (CWV)?
Core Web Vitals (CWV) are Google's three field-measured performance metrics: LCP, INP, CLS. See [[seo/core-web-vitals]].
### What is LCP (Largest Contentful Paint)?
LCP (Largest Contentful Paint) is the time to render the largest above-the-fold element. Target under 2.5 seconds at p75. See [[glossary/lcp]].
### What is INP (Interaction to Next Paint)?
INP (Interaction to Next Paint) is the time from a user interaction to the next visual response. Replaced FID in 2024. Target under 200ms at p75. See [[glossary/inp]].
### What is CLS (Cumulative Layout Shift)?
CLS (Cumulative Layout Shift) is a visual stability metric measuring unexpected layout shifts. Target under 0.1 at p75. See [[glossary/cls]].
### What is TTFB (Time to First Byte)?
TTFB (Time to First Byte) is server response time. Foundational but not a CWV. Target under 800ms. See [[seo/page-speed]].
### What is FCP (First Contentful Paint)?
FCP (First Contentful Paint) is the time to render any content on screen. Not a CWV but tracked in CrUX.
### What is CrUX (Chrome User Experience Report)?
CrUX (Chrome User Experience Report) is Google's public field-data dataset for Core Web Vitals. The ground truth for CWV at p75.
### What is Lighthouse?
Lighthouse is Google's lab tool for measuring performance, accessibility, SEO, and best practices. Lab data, not field data; use for development, not ranking decisions.
## AI search and agent readability
### What is AEO (Answer Engine Optimization)?
AEO (Answer Engine Optimization) is the practice of structuring content so AI engines can extract and cite it. See [[seo/answer-engine-optimization]].
### What is GEO (Generative Engine Optimization)?
GEO (Generative Engine Optimization) is a synonym for AEO. The newer term that emphasizes generative AI engines (Google AI Overviews, ChatGPT, Perplexity, Claude). See [[seo/generative-engine-optimization]].
### What is an AI Overview?
An AI Overview is Google's AI-generated SERP summary that appears above traditional results for many queries. Inclusion depends on entity recognition, citation hygiene, and structured definitions.
### What is llms.txt?
llms.txt is a markdown file at the site root listing the canonical pages in a way agents can ingest cheaply. See [[seo/llms-txt]].
### What is llms-full.txt?
llms-full.txt is a companion to llms.txt containing the full text of priority pages, concatenated for one-shot agent ingestion. See [[seo/discoverability-files]].
### What is ai.txt?
ai.txt is a proposed standard declaring AI training opt-in or opt-out at the domain level. See [[seo/ai-txt]].
### What are GPTBot, ClaudeBot, PerplexityBot?
GPTBot, ClaudeBot, and PerplexityBot are the crawlers run by OpenAI, Anthropic, and Perplexity respectively. Each respects robots.txt and ai.txt by convention.
### What is entity SEO?
Entity SEO is the practice of building a recognized entity in the search engine's knowledge graph (author, brand, product). See [[seo/author-entities]].
### What is a knowledge graph?
A knowledge graph is the search engine's structured database of entities and their relationships. Inclusion drives knowledge-panel SERP features.
## Content strategy
### What is topical authority?
Topical authority is the depth and breadth of a site's coverage on a given topic cluster. Built by shipping comprehensive content on a focused subject. See [[seo/content-clusters]].
### What is a content cluster?
A content cluster is a pillar page plus supporting cluster pages, all internally linked. The unit of topical authority. See [[seo/content-clusters]].
### What is a pillar page?
A pillar page is the hub page of a content cluster. Comprehensive coverage of the parent topic, linking out to cluster pages for sub-topics.
### What is a cluster page?
A cluster page is a supporting page within a content cluster. Targets a specific long-tail keyword and links back to the pillar.
### What is E-E-A-T?
E-E-A-T stands for Experience, Expertise, Authoritativeness, Trustworthiness. Google's quality framework used by human raters and modeled by the ranking systems. See [[seo/e-e-a-t]].
### What is HCS (Helpful Content System)?
HCS (Helpful Content System) is Google's classifier that grades whole sites on people-first vs. search-engine-first content. Site-wide signal. See [[seo/helpful-content-update]].
### What is a content refresh?
A content refresh is updating an existing page with new facts, new sections, or new framing. Distinct from a date-only update. See [[seo/content-refresh]].
### What is YMYL (Your Money, Your Life)?
YMYL (Your Money, Your Life) refers to topics where bad information could harm finances, health, or safety. Held to a higher E-E-A-T bar.
### What is helpful content (people-first content)?
Helpful content (people-first content) is Google's term for content written to answer the searcher's question rather than to rank. The opposite is search-engine-first content. See [[seo/helpful-content-update]].
## Discoverability files
### What are discoverability files?
Discoverability files are the collective set of special files a public site ships at the root or under `/.well-known/`: robots.txt, sitemap.xml, llms.txt, ai.txt, security.txt, humans.txt, manifest.json, IndexNow key, OG default, favicon. See [[seo/discoverability-files]].
### What is security.txt?
security.txt is a file at `/.well-known/security.txt` declaring vulnerability disclosure contacts. RFC 9116.
### What is humans.txt?
humans.txt is an informal file at `/humans.txt` crediting the team behind the site.
### What is manifest.json?
manifest.json is a PWA configuration file declaring app name, icons, theme color, display mode.
### What is IndexNow?
IndexNow is a protocol for instantly notifying search engines (Bing, Yandex) of content changes. See [[seo/indexnow]].
### What is an IndexNow key?
An IndexNow key is a random hex string (8 to 128 characters) proving ownership of the domain, served as `/<key>.txt`. See [[seo/indexnow]].
### What is an OG image?
An OG image is the `og:image` meta tag image used in social previews. Standard size 1200x630. See [[seo/og-images]].
## SERP features
### What is a featured snippet?
A featured snippet is a position-zero result displaying a direct answer above the first organic result. See [[seo/serp-features]].
### What is People Also Ask (PAA)?
People Also Ask (PAA) is the expandable question-and-answer accordion in mid-SERP. Google sources PAA answers from visible page content that reads as Q&A, not from FAQPage JSON-LD. See [[seo/serp-features]].
### What is a knowledge panel?
A knowledge panel is the right-rail entity card displaying structured information about a person, place, or thing. Driven by the knowledge graph.
### What are sitelinks?
Sitelinks are the indented sub-links shown under a brand's main result for branded queries. Algorithmic; cannot be requested directly.
### What is an image pack?
An image pack is a horizontal strip of image results within the main SERP. Driven by image SEO.
### What is a video carousel?
A video carousel is a horizontal strip of video results, usually from YouTube. Requires VideoObject schema.
### What is a local pack?
A local pack is the map plus three-business listing for local queries. Driven by Google Business Profile. See [[seo/local-seo]].
## Penalties and recovery
### What is a manual action?
A manual action is a penalty applied by a Google human reviewer. Notified in GSC. Requires explicit reconsideration request to clear.
### What is an algorithmic penalty?
An algorithmic penalty is a ranking downweight applied by the algorithm, not a human. No notification; detected by traffic patterns.
### What is a core update?
A core update is a broad change to the ranking algorithm. Announced retroactively by Google. May reshuffle rankings significantly.
### What is a reconsideration request?
A reconsideration request is the form a site submits to ask Google to review a manual action. Required after fixing the underlying issue.
### What is a toxic backlink?
A toxic backlink is a link from a low-quality, spammy, or unrelated site. Disavow if numerous; ignore if isolated.
## Local SEO
### What is Google Business Profile (GBP)?
Google Business Profile (GBP) is the free Google product for managing a business's local listing. Formerly Google My Business. See [[seo/local-seo]].
### What is NAP?
NAP stands for Name, Address, Phone. Must be identical across the site, GBP, and major citation sites.
### What is a local pack (Local SEO context)?
A local pack in the Local SEO context is the same SERP feature defined above. See SERP features above.
### What is a citation?
A citation is a mention of a business's NAP on another site (Yelp, Bing Places, industry directories). Citations strengthen local relevance.
### What is LocalBusiness schema?
LocalBusiness schema is the JSON-LD type for a physical business. Includes hours, address, geo coordinates, payment types.
## Analytics and tooling
### What is Google Search Console (GSC)?
Google Search Console (GSC) is Google's free tool for monitoring a site's search performance, coverage, and structured data. The primary SEO instrument. See [[howto/master-google-search-console]].
### What is Bing Webmaster Tools?
Bing Webmaster Tools is Microsoft's equivalent for Bing. Always pair with GSC.
### What is CTR (Click-Through Rate)?
CTR (Click-Through Rate) is the percentage of SERP impressions that result in a click. The primary lever for title and meta-description testing.
### What are impressions?
Impressions are the number of times a page appeared in the SERP for a query. Measured in GSC.
### What is average position?
Average position is the mean SERP position a page held for a query in a given period. Measured in GSC.
### What is bounce rate?
Bounce rate is the percentage of sessions that ended without further interaction. Misleading on single-page intent; favor engagement metrics.
### What is engagement rate?
Engagement rate is GA4's primary engagement metric. Replaces bounce rate.
### What is a schema validator?
A schema validator is a tool that parses and checks structured-data markup. Google's Rich Results Test is the canonical one.
### What is Lighthouse CI?
Lighthouse CI is continuous-integration automation for Lighthouse. Runs on every build.
### What are Screaming Frog and Sitebulb?
Screaming Frog and Sitebulb are two desktop SEO crawlers used for site audits. Either is acceptable for the full audit workflow described in [[seo/audit-checklist]].
## Related
- [[seo/technical]]
- [[seo/content]]
- [[seo/structured-data]]
- [[seo/ai-search-optimization]]
- [[seo/discoverability-files]]
- [[seo/helpful-content-update]]
- [[seo/e-e-a-t]]
- [[seo/audit-checklist]]