# Glossary: llms.txt, GEO, AEO and AI crawler terms > Short definitions of AI search terms: GEO, AEO, LLMO, AI SEO, AI Overviews, agent, crawler, llms.txt, structured data, Schema.org, JSON-LD, with origin and status Page: https://llms-full-txt.ru/en/reference/glossary/ Site index: https://llms-full-txt.ru/en/llms.txt This subject has many words, and they are not equal. Some are fixed in documents and code, some were coined by service vendors, some are product names. Each term below carries a status: where the word came from and whether it can be relied on. document or standard · proposal · convention · research paper · vendor word ## Files and formats ### llms.txt proposal A text file at the root of a site: a name, a short summary and lists of links to the main material. Written for an AI agent. Proposed by Jeremy Howard in September 2024; the [second edition](https://llmstxt.org/) came out on August 10, 2026. It is not an IETF or W3C standard. More: [What is llms.txt](https://llms-full-txt.ru/en/guides/what-is-llms-txt/), [the format](https://llms-full-txt.ru/en/specification/format/). ### llms-full.txt convention A file with the full text of a site's material in one document. It is not in the `llms.txt` proposal: documentation platforms established the name. More: [What is llms-full.txt](https://llms-full-txt.ru/en/guides/llms-full-txt/). ### robots.txt standard A file with access rules for robots, described in RFC 9309. It says where robots may go, not what is useful. More: [AI crawlers and robots.txt](https://llms-full-txt.ru/en/guides/ai-crawlers/). ### sitemap.xml standard A list of site addresses for search robots. It helps discover pages and does not rate their importance. ### Markdown convention A simple text format: headings, lists, links and tables are marked with ordinary characters. Convenient for a person and for a program. More: [Markdown versions of pages](https://llms-full-txt.ru/en/guides/markdown-pages/). ### Structured data search engine documentation A machine-readable description of a page: what is on it and which properties it has. More: [Structured data and JSON-LD](https://llms-full-txt.ru/en/guides/json-ld/). ### Schema.org shared vocabulary A vocabulary of types and properties for structured data: `Product`, `Article`, `Organization`, `price`, `author`. Founded in 2011 by the search engines Google, Bing, Yahoo and Yandex. ### JSON-LD W3C recommendation A format for writing structured data: a separate block in the page code. Google recommends it. The other formats are Microdata and RDFa. ## Programs ### Crawler owner documentation A program that walks sites and downloads pages. AI companies run crawlers of three classes: for model training, for a search index, and for a specific user's request. More: [AI crawlers and robots.txt](https://llms-full-txt.ru/en/guides/ai-crawlers/). ### AI agent convention A program built on a language model that searches, reads pages and performs actions on a person's request. It differs from a crawler in that it comes for the answer to a specific question. ### MCP open protocol Model Context Protocol - a protocol through which an AI application connects to external data and tools. It is not directly related to `llms.txt`. More: [llms.txt and MCP](https://llms-full-txt.ru/en/reference/mcp-relationship/). ### Context convention The amount of text a model can take into account at once. It is limited, which is why short maps and clean text without service markup suit an agent. ## Optimization and measurement ### GEO research paper Generative Engine Optimization - optimization for generative search systems. The term was introduced in a [2023 research paper](https://arxiv.org/abs/2311.09735). What is measured is the share and position of a source in an answer. More: [GEO and AEO](https://llms-full-txt.ru/en/guides/geo-aeo/). ### AEO vendor word Answer Engine Optimization - optimization for systems that answer rather than return a list of links. Its origin is attributed to 2017; the primary source is not confirmed. ### LLMO vendor word Large Language Model Optimization. Used as a synonym of GEO. No primary source was found. ### AI SEO vendor word An ambiguous term. The first meaning is using AI in SEO work. The second is working on a site's presence in AI answers. Without clarification it is unclear which one is meant. ### AI visibility vendor word An umbrella name for a site's presence in AI answers. It is not measured as such: bot requests, referrals, citations and share of voice are. More: [How to measure AI visibility](https://llms-full-txt.ru/en/guides/ai-visibility/). ### Share of voice convention The share of answers that name a site or a brand over a fixed set of questions. A comparative metric. ### Citation convention A link to a site in an AI answer as a source of facts. ## Products and names ### AI Overviews product name A block with an answer above the results in Google Search. [Introduced on May 14, 2024](https://blog.google/products/search/generative-ai-google-search-may-2024/). Search Console has no separate breakdown for it. ### AI Mode product name A mode of Google Search with a dialog instead of a list of links. [Introduced on March 5, 2025](https://blog.google/products/search/ai-mode-search/). ### Agentic web vendor word The idea of a web where agents, not people, perform a large share of actions. [Microsoft brought the word into use in May 2025](https://blogs.microsoft.com/blog/2025/05/19/microsoft-build-2025-the-age-of-ai-agents-and-building-the-open-agentic-web/). ### Agentic Browsing category name An experimental category of audits in Lighthouse that includes the `llms.txt` audit. More: [Lighthouse and llms.txt](https://llms-full-txt.ru/en/guides/lighthouse/). ## What Google calls all this In its guide [Google writes](https://developers.google.com/search/docs/fundamentals/ai-optimization-guide) that AEO and GEO are terms you may see used, while optimizing for AI features of Search is still SEO. The company does not treat it as a separate discipline.