Glossary

Short, plain definitions of the terms that matter in search and AI answers.

AEO (answer engine optimisation)answer engine optimisation, answer engine optimization: AEO is the practice of shaping content so that a search engine or AI system can use it as the direct answer to a question, in featured snippets, voice answers or AI-generated responses.
AI Mode: AI Mode is a conversational mode of Google Search that answers a question with an AI-written response, accepts follow-up questions and links to the web pages that support the answer.
AI OverviewsAIO: AI Overviews are AI-generated summaries that Google Search shows at the top of results for some queries, with links to the web pages that support the answer.
Canonical URLcanonical, rel=canonical: A canonical URL is the one address a search engine selects to represent a set of duplicate or very similar pages, and the version it shows in search results.
Citation (in AI answers)supporting link, source link, AI citation: A citation in an AI answer is a link or named source that an AI system shows as support for its generated response, such as the supporting links in Google AI Overviews or the sources listed by Copilot, ChatGPT and Perplexity.
Crawl budgetcrawl capacity, crawl demand: Crawl budget is the set of URLs a search engine can and wants to crawl on a site, set by how much crawling the server can handle (crawl capacity) and how much the engine wants the content (crawl demand).
E-E-A-TE-A-T, EEAT: E-E-A-T stands for experience, expertise, authoritativeness and trustworthiness: the qualities Google trains its search quality raters to look for when judging whether content is reliable and helpful.
GEO (generative engine optimisation)generative engine optimisation, generative engine optimization: GEO is the practice of increasing how often and how prominently a source is used or cited in answers written by generative AI systems such as AI Overviews, AI Mode, ChatGPT, Gemini and Perplexity.
Indexingindex: Indexing is the stage in which a search engine analyses a page it has crawled and stores it in its index, the database it draws on to answer queries. A page that is not indexed cannot appear in results.
llms.txt: llms.txt is a proposed Markdown file at the root of a website that lists its most useful pages with short notes, so language models and AI agents can find clean content when answering a question.
Query fan-outfan-out queries: Query fan-out is a technique in which an AI search system turns one question into several related searches, runs them at the same time and combines what it finds into a single answer.
SEOsearch engine optimisation, search engine optimization: SEO (search engine optimisation) is the work of making a website easy for search engines to crawl, index and understand, so its pages can rank in results and be chosen by searchers.
Structured dataschema markup, schema.org markup: Structured data is code added to a page, usually JSON-LD using the schema.org vocabulary, that describes the page's content in a standard format so search engines can classify it and show rich results.
Zero-click searchno-click search: A zero-click search is a search that ends without the user clicking through to any website, because the answer was shown on the results page or the user searched again or left.