AEO (Answer Engine Optimization)
The practice of structuring a website so AI systems — ChatGPT, Perplexity, Claude, Google AI Overviews — cite it as a source when generating an answer. The AI-search equivalent of SEO, with a different judge (a language model synthesizing an answer, not a ranking algorithm sorting links) and different winning formats (short, direct, extractable claims rather than comprehensive topic coverage).
GEO (Generative Engine Optimization)
Functionally the same practice as AEO, used more or less interchangeably. "Generative" emphasizes that the output is a generated answer rather than a retrieved list of links; "Answer" emphasizes the end result the user sees. Neither term has fully won out yet — you'll see both used for the same thing, sometimes by the same source in the same article.
LLMO (Large Language Model Optimization)
A less common third term for the same general practice, emphasizing optimization for the large language models themselves (ChatGPT, Claude, Gemini) rather than the search-engine framing of AEO/GEO. Used less frequently than AEO or GEO as of 2026, but you'll occasionally see it.
AI Overview
Google's AI-generated summary that appears above traditional search results for many queries, synthesizing an answer from a small set of sources and citing 3-5 of them. Distinct from a featured snippet (a single quoted passage from one source) — an AI Overview is generated text drawing on multiple sources at once.
Citation (in the AEO context)
When an AI system names or links your site as a source for a claim in its generated answer. The core unit of success in AEO — there's no equivalent to a search ranking position, just whether you were cited for a given query or not.
Answer engine
Any AI system that responds to a query with a synthesized, generated answer rather than a list of links — ChatGPT, Perplexity, Claude, and Google's AI Overviews all qualify. Contrasted with a traditional search engine, which returns ranked links for the user to click through themselves.
Structured data / schema markup
Machine-readable markup added to a webpage (using the schema.org vocabulary) that explicitly labels what a piece of content is — a product, an FAQ, an organization, an article. Gives AI systems (and traditional search engines) an explicit version of your content's meaning instead of requiring them to infer it from prose, which meaningfully improves citation odds.
llms.txt
A proposed plain-text file, placed at a site's root (like robots.txt), that describes what a website is and does in language written specifically for AI crawlers to parse. Newer and less universally adopted than schema markup, but a cheap, direct signal aimed squarely at how AI systems evaluate a site's purpose.
Zero-click search
A search where the user gets their answer directly in the search results (via a featured snippet or AI Overview) without clicking through to any website. AI Overviews accelerate this trend — which is exactly why citation (being the source an AI names, even without a click) matters as its own goal, separate from traditional click-driven SEO traffic.
Featured snippet
A single quoted passage pulled from one source and displayed prominently above traditional search results — Google's pre-AI-Overview mechanism for zero-click answers. Featured-snippet optimization techniques (direct answers, clear structure) substantially overlap with AEO techniques, since both reward the same kind of extractable, self-contained content.
RAG (Retrieval-Augmented Generation)
The technical mechanism most AI answer engines use under the hood: retrieve a small set of relevant documents (via search), then generate an answer grounded in those retrieved documents rather than purely from the model's training data. Understanding RAG explains why AEO works the way it does — a page has to first be retrieved (which favors pages that already rank/index well) before it can be cited, which is why AEO and traditional SEO aren't actually competing disciplines.
Where to go from here
If you want the practical, structural version of these definitions rather than just the vocabulary: how to check if ChatGPT cites your site, AEO vs SEO in practice, and why sites get skipped by Google AI Overviews all cover specific, actionable fixes. Or just test one real query against your own site for free and see where you actually stand.