In one sentence
Answer Engine Optimization (AEO) is the practice of making a brand visible, accurately described and cited inside the answers that AI systems such as ChatGPT, Google AI Overviews, Gemini, Claude and Perplexity generate, rather than only ranking in a list of links.
Classic search ends with ten links and the user decides. An answer engine ends with a written paragraph that names two or three brands and cites a handful of sources. Only the brands inside that paragraph get considered, so the unit of success shifts from a position on a page to a sentence inside an answer.
AEO work splits into three jobs. Measurement: knowing which prompts your buyers ask, whether you are named, where you rank inside the answer and which pages get cited. Content: publishing pages that answer those questions directly, in the self-contained form models can lift. Technical: making sure AI crawlers can fetch and parse your pages at all.
AEO and GEO describe the same discipline from different angles, and in practice teams use the terms interchangeably.