- 70 SEO terms, A to Z, each defined in one to three plain sentences.
- Every term has its own link, such as /seo-glossary#noindex, so you can share a single definition.
- Each definition ends with a Learn more link to the guide or free tool that covers the term in depth.
0-9
301 redirect
A permanent redirect: the server answers with HTTP status 301 and sends visitors and crawlers to a new URL. Search engines treat it as a strong signal that the new URL should replace the old one in results. Learn more: 301 vs 302 redirects
302 redirect
A temporary redirect (HTTP status 302). It tells search engines the move is short-term, so they usually keep showing the original URL. Learn more: 301 vs 302 redirects
404 error
The HTTP status a server returns when a page does not exist. A few 404s are normal; internal links that point to them are broken links worth fixing. Learn more: Broken links: find and fix them
A
AI crawler
A bot run by an AI company, such as GPTBot, ClaudeBot or PerplexityBot, that fetches pages to train models or to answer questions in AI search. You can allow or block each one by its user agent in robots.txt. Learn more: Allow or block AI crawlers in robots.txt
AI Overviews
AI-generated summaries that Google shows above some search results, with links to the pages they draw on. Learn more: How to get cited in AI Overviews
Alt text
The alt attribute on an image: a short text description read aloud by screen readers and used by search engines to understand the image. Purely decorative images should have an empty alt. Learn more: Image alt text guide
Anchor text
The visible, clickable words of a link. Descriptive anchor text tells readers and search engines what the linked page is about. Learn more: Internal linking for SEO
Average position
A Search Console metric: the average of your site's topmost position each time it appeared in Google's results. Lower is better, and 1 is the first result. Learn more: Search Console average position explained
B
Backlink
A link from another website to yours. Search engines follow links to discover pages, and Google uses them as one of many signals of a page's importance. Learn more: What are backlinks?
Bing Webmaster Tools
Microsoft's free service for site owners. It shows how Bing crawls and indexes your site and the searches you appear for, and lets you submit sitemaps and URLs. Learn more: Bing Webmaster Tools guide
Breadcrumb
A row of links showing where a page sits in a site's structure, such as Home / Blog / Guide. BreadcrumbList structured data describes that path to search engines. Learn more: Schema markup generator
Broken link
A link that leads to an error page, usually a 404, or to a domain that no longer works. Broken links waste visitors' clicks and crawlers' time. Learn more: Broken link checker
C
Canonical tag
A <link rel="canonical"> element that names the preferred URL when the same or very similar content is reachable at several URLs. Google treats it as a strong hint, not a command. Learn more: Canonical tags guide
Cumulative Layout Shift (CLS)
The Core Web Vital for visual stability: how much visible content moves unexpectedly while a page is open. A score of 0.1 or less is good. Learn more: Core Web Vitals thresholds
Common Crawl
A non-profit that crawls the web and publishes its data free for anyone to use. Its link data is one public source for backlink research. Learn more: How to check backlinks
Core Web Vitals
Google's three page-experience metrics, measured from real Chrome users: Largest Contentful Paint (loading), Interaction to Next Paint (responsiveness) and Cumulative Layout Shift (visual stability). Learn more: Core Web Vitals thresholds
Crawl budget
The number of URLs a search engine can and wants to crawl on a site in a given time. Google says it mainly matters for very large or fast-changing sites. Learn more: Crawled and discovered but not indexed
Crawled - currently not indexed
A Search Console status: Google fetched the page but decided not to index it for now. It may or may not be indexed later. Learn more: Crawled and discovered but not indexed
Crawling
The step where a search engine's bot fetches pages, finding new URLs through links and sitemaps. A page that is never crawled cannot be indexed. Learn more: How search engines work
D
Discovered - currently not indexed
A Search Console status: Google knows the URL exists but has not crawled it yet, typically because it rescheduled the crawl to avoid overloading the site. Learn more: Crawled and discovered but not indexed
Domain age
How long a domain has been registered. Google's representatives have said domain age by itself is not a ranking factor; older sites tend to rank because of the links and history they have built. Learn more: Does domain age matter for SEO?
Domain authority
A 0-100 score from the SEO tool Moz that predicts how well a domain might rank, based mainly on its links. Other tools have similar scores. Google does not use any of them. Learn more: What is domain authority?
Domain Rating (DR)
Ahrefs' 0-100 score for the strength of a domain's backlink profile. Like Moz's domain authority, it is a third-party metric, not a Google one. Learn more: What is domain authority?
Duplicate content
The same or very similar content at more than one URL. Google groups the copies and shows one version; canonical tags and redirects tell it which one you prefer. Learn more: Canonical tags guide
G
Generative engine optimization (GEO)
Work aimed at getting a brand or page cited in answers written by AI tools such as ChatGPT, Perplexity, Gemini and Google's AI Overviews. Learn more: Generative engine optimization
Google algorithm update
A change Google makes to how its systems rank results. Broad "core updates" and spam updates are announced on the Google Search Status Dashboard. Learn more: Google algorithm updates in 2026
Google Keyword Planner
A free keyword tool inside Google Ads that shows keyword ideas and search volume. It needs a Google Ads account. Learn more: Is Google Keyword Planner free?
Google Search Console
Google's free service for site owners. It shows the searches your site appears for, with clicks, impressions and average position, plus which pages are indexed and why others are not. Learn more: Free rank tracker
Googlebot
The name of Google's web crawler, the program that fetches pages for Google Search. Learn more: How search engines work
H
Heading tags (H1-H6)
HTML headings that outline a page. One clear H1 naming the topic, with H2 and H3 headings for its sections, helps readers and search engines follow it. Learn more: On-page SEO checklist
Hreflang
An annotation that tells search engines which language or regional version of a page to show to which users. Every version should list all the others and itself. Learn more: Hreflang tags guide
HTTP status code
The three-digit code a server sends with every response: 2xx means success, 3xx a redirect, 4xx a client error such as 404, and 5xx a server error. Learn more: HTTP header checker
I
Impressions
A Search Console metric: how many times a link to your site appeared in search results. A result counts as an impression even if the searcher does not click it. Learn more: Search Console average position explained
Indexability
Whether a page can be added to a search index: it returns HTTP 200, robots.txt lets crawlers fetch it, it carries no noindex, and its canonical points to itself. Learn more: Indexability checker
Indexing
The step where a search engine analyses a page it has fetched and stores it in its index, so the page can appear in results. Learn more: How search engines work
IndexNow
An open protocol that lets a site tell participating search engines, Bing among them, as soon as URLs are added, changed or deleted. Learn more: Bing Webmaster Tools guide
Interaction to Next Paint (INP)
The Core Web Vital for responsiveness: how quickly a page visibly reacts to clicks, taps and key presses. 200 milliseconds or less is good. Learn more: Core Web Vitals thresholds
Internal link
A link from one page to another page on the same website. Internal links help visitors and crawlers find pages and show which pages matter most. Learn more: Internal linking for SEO
K
Keyword cannibalization
When several pages on one site target the same search, so they compete with each other and none ranks as well as one strong page could. Learn more: Keyword cannibalization guide
Keyword clustering
Grouping keywords that share the same search intent, so one page can target the whole group instead of one page per keyword. Learn more: Keyword clustering guide
Keyword density
How often a word or phrase appears, as a share of all the words on a page. There is no ideal percentage; write for readers rather than a target. Learn more: Keyword density checker
Keyword difficulty
An SEO tool's 0-100 estimate of how hard it is to reach the top results for a keyword, usually based on the pages already ranking. Each tool calculates it differently. Learn more: What is keyword difficulty?
Keyword research
Finding the searches your audience makes, with their volume and intent, and choosing which ones each page should target. Learn more: How to do keyword research
L
Largest Contentful Paint (LCP)
The Core Web Vital for loading: how long the largest image or text block in view takes to appear. 2.5 seconds or less is good. Learn more: Core Web Vitals thresholds
llms.txt
A proposed Markdown file at /llms.txt that summarizes a site and lists the pages an AI tool should read first. Google says Google Search ignores it. Learn more: What is llms.txt?
Long-tail keyword
A longer, more specific search phrase. Each one is searched less often, but together they add up, and the intent is usually clearer. Learn more: Long-tail keywords guide
M
Model Context Protocol (MCP)
An open protocol that lets AI assistants such as Claude connect to outside tools and data sources, for example SEO data. Learn more: SEO MCP servers
Meta description
A short HTML summary of a page. Google may show it as the snippet under the title in results, but it often writes its own from the page text. Learn more: Title tag and meta description length
N
Nofollow
A rel="nofollow" value on a link that asks search engines not to pass credit to the linked page. Google treats it, and the related "sponsored" and "ugc" values, as hints. Learn more: What are backlinks?
Noindex
A rule, set in a robots meta tag or an X-Robots-Tag header, telling search engines not to show a page in results. Crawlers must be allowed to fetch the page to see it. Learn more: X-Robots-Tag guide
O
On-page SEO
Improving the parts of a page you control directly: its title, headings, content, images, internal links and structured data. Learn more: On-page SEO checklist
Open Graph
Meta tags such as og:title, og:description and og:image that control how a link looks when it is shared on social networks and in chat apps. Learn more: Open Graph tags guide
Orphan page
A page that no other page on the same site links to, so visitors and crawlers struggle to find it. Learn more: Orphan pages guide
P
PageRank
Google's original algorithm for scoring pages by the links pointing to them. Google still uses link signals, but the public PageRank score is no longer shown. Learn more: What are backlinks?
R
Rank tracking
Checking where your pages rank for chosen keywords over time, so you can see the effect of changes and updates. Learn more: How to track keyword rankings
Redirect chain
Two or more redirects in a row before a visitor reaches the final URL. Each hop adds delay, so links should point straight at the final address. Learn more: 301 vs 302 redirects
Referring domain
A separate website that links to yours at least once. A hundred links from one site still count as one referring domain. Learn more: How to check backlinks
Rich results
Search results with extra features, such as product prices or event dates, that a search engine can show when a page has suitable structured data. Learn more: Schema markup guide
Robots.txt
A text file at the root of a site that tells crawlers which paths they may fetch. It controls crawling, not indexing: a blocked URL can still be indexed if other pages link to it. Learn more: Robots.txt guide
S
Schema markup
Structured data, usually JSON-LD using the schema.org vocabulary, that describes what a page is about (an article, a product, an event) in a form search engines can read. Learn more: Schema markup guide
Search intent
The goal behind a search: to learn something (informational), reach a site (navigational), compare options (commercial) or buy (transactional). Learn more: Search intent guide
Search volume
How many times a keyword is searched in a typical month, usually shown as an average or a range. Learn more: How to find keyword search volume
SEO
Search engine optimization: making a website easy for search engines to find, understand and trust, so it shows up in the unpaid results for relevant searches. Learn more: What is SEO?
SEO audit
A structured check of a website for problems that hold back its search performance, from crawling and indexing errors to titles, content and links. Learn more: How to do an SEO audit
SERP snippet
The block a search engine shows for one result on the search engine results page (SERP): usually a title link, the URL and a short description. Learn more: SERP snippet preview
Site reputation abuse
A Google spam policy against publishing third-party pages on a site to take advantage of that site's ranking signals. Learn more: Google's site reputation policy update
Soft 404
A page that tells visitors it does not exist, or has almost no content, while still returning HTTP 200. Google reports these in Search Console and usually leaves them out of its index. Learn more: Broken links: find and fix them
T
Title tag
The <title> element of a page. Search engines usually use it as the clickable headline in results, and browsers show it on the tab. Learn more: Title tag and meta description length
X
X-Robots-Tag
An HTTP response header that carries the same rules as the robots meta tag, such as noindex. It also works for files without HTML, like PDFs and images. Learn more: X-Robots-Tag guide
XML sitemap
A file that lists the URLs you want search engines to crawl, optionally with the date each one last changed. It helps discovery but does not guarantee indexing. Learn more: XML sitemap guide
Sources
- Google Search Central: Search Engine Optimization (SEO) Starter Guide — the basics behind most of these terms
- Google Search Central: In-depth guide to how Google Search works — crawling, indexing and serving
- Search Console Help: Page indexing report — indexing statuses such as crawled or discovered but not indexed
- web.dev: Web Vitals — LCP, INP and CLS and their thresholds
- Bing Webmaster Guidelines — how Bing finds, indexes and ranks pages
- IndexNow — the IndexNow protocol
- schema.org: DefinedTermSet — the vocabulary used for this page's structured data
