Glossary

The language of AI search, defined

Plain-language definitions of the AEO and AI-search terms that matter — answer engines, llms.txt, E-E-A-T, AI citations, and more.

Answer Engine Optimization (AEO)

Answer Engine Optimization (AEO) is the practice of structuring a website’s content and technical signals so that AI assistants — ChatGPT, Claude, Perplexity, Gemini, and Google AI Overviews — cite it when answering questions in its domain. Where classic SEO competes for a ranked position on a results page, AEO competes to be quoted inside the AI’s answer itself.

Read the full definition →

Generative Engine Optimization (GEO)

Generative Engine Optimization (GEO) is the practice of optimizing content so that generative AI systems — ChatGPT, Perplexity, Google AI Overviews, and other LLM-powered search experiences — include and cite it when synthesizing answers. GEO and Answer Engine Optimization (AEO) are two names for substantially the same discipline.

Read the full definition →

Answer engine

An answer engine is a search system that responds to a question with a direct, synthesized answer — usually generated by a large language model and backed by cited sources — instead of a ranked list of links. ChatGPT with search, Perplexity, Google AI Overviews, and Claude with web access are all answer engines.

Read the full definition →

llms.txt

llms.txt is a plain-markdown file served at a website’s root (example.com/llms.txt) that gives AI systems a curated, LLM-friendly map of the site: what it is, and which pages best represent it. Where robots.txt tells crawlers what they may not access, llms.txt tells AI crawlers what is most worth reading.

Read the full definition →

E-E-A-T

E-E-A-T stands for Experience, Expertise, Authoritativeness, and Trustworthiness — the framework from Google’s Search Quality Rater Guidelines for judging whether content deserves to rank, and increasingly, whether AI answer engines consider it safe to cite. It is demonstrated on the page, not asserted: bylines, credentials, first-hand evidence, citations, and a resolvable organization behind the site.

Read the full definition →

AI citation

An AI citation is an attribution inside an AI-generated answer — a link, footnote, or named mention that credits a website as the source of a claim. Citations are the currency of AI search: they are how a site is visible at all inside ChatGPT, Perplexity, or Google AI Overviews, and they carry the referral traffic and brand trust that ranked links used to.

Read the full definition →

Structured data (JSON-LD)

Structured data is machine-readable markup — on the modern web, almost always JSON-LD using schema.org vocabulary — embedded in a page to state unambiguously what the page is about: who published it, who wrote it, what it answers, and how its entities relate. It is the layer search and answer engines read when they need facts rather than prose.

Read the full definition →

AI crawler

An AI crawler is a bot that fetches web content on behalf of an AI system — for training, for live retrieval when a user asks a question, or both. The ones that matter most for visibility are GPTBot and OAI-SearchBot (OpenAI), ClaudeBot (Anthropic), PerplexityBot, and Google-Extended (Google’s AI training control). Each identifies itself by user-agent and respects robots.txt.

Read the full definition →