AI search glossary
This glossary defines the terms used in AI search optimization in plain words. Each entry gives a one-sentence definition, the status of the idea (standard, draft or vendor feature) and links to the primary source.
By SeenLens · Last updated
How to read an entry
Each entry starts with the definition. It then says who proposed the idea and when, whether any search engine or AI system is documented to use it, and how to check it on your own site. Related terms link to each other, and crawler names have their own pages in the AI crawler list.
Status labels
| Status | Meaning | Example |
|---|---|---|
| Standard | Published by a standards body such as the IETF or W3C | robots.txt (RFC 9309), HTTP content negotiation (RFC 9110) |
| Draft or proposal | Written up in public, not yet a standard, may change | llms.txt, WebMCP, Content Signals |
| Vendor feature | Defined by one company for its own product | Bing grounding queries, Google AI Mode query fan-out |
| Industry term | A name people use for a practice, with no formal definition | AI visibility, GEO, AEO |
The status matters because a standard is read by many systems, while a proposal may be read by none. Where no search engine or AI assistant documents that it uses an idea, the entry says so. For the practical side of each term, follow the links to the guides and fix guides.
Pages in this section
- llms.txt
Definition of llms.txt: a proposed Markdown index file for AI tools, its format, and the evidence on who reads it.
- AI visibility
Definition of AI visibility: readiness versus measured mentions, and the free reports that show real data.
- Content signals
Definition of Content Signals: the robots.txt line for search, ai-input and ai-train, with syntax and limits.
- Query fan-out
Definition of query fan-out: how AI search splits one question into many searches, with Google's wording.
- Grounding queries
Definition of grounding queries: the phrases AI used to retrieve your content, as reported by Bing Webmaster Tools.
- Markdown content negotiation
Definition of Markdown content negotiation: Accept text/markdown, Vary: Accept, and who sends the header.