Resources · Glossary

The AI search glossary, defined plainly.

Some of these terms are established. Some are new and still argued over. Each is defined the way we use it.

A

AEO (Answer Engine Optimization): An industry label for structuring content so search-results features extract and credit your answer: AI Overviews and AI Mode, featured snippets, People Also Ask and voice assistants. At Underneath this work is part of every GEO program.
AI Mode: Google’s conversational AI search mode: it answers a query with a generated response and cited links, and takes follow-up questions. It often cites different sources from AI Overviews for the same search.
AI Overviews: Google’s AI-generated summaries shown at the top of some search results, typically citing several source pages.
AI share of voice: Your brand’s mentions as a share of all tracked brand mentions across the buyer prompt set.
AI visibility: How often, and how accurately, a business appears in AI-generated answers: Google AI Overviews and AI Mode, ChatGPT, Gemini, Perplexity and Copilot. Measured with a fixed buyer prompt set run on a schedule.
Answer accuracy: The share of statements an AI system makes about a brand that are factually correct and current.

Buyer prompt set: The fixed list of real buyer questions we run across the tracked engines on a stated schedule to measure visibility in AI answers. Also called a prompt universe. Asking to see one is a useful test when choosing a GEO agency.

Canonical URL: The preferred version of a page declared to search engines when similar or duplicate URLs exist.
Citation rate: How often AI-generated answers cite a brand’s owned pages as sources.
Crawl budget: The number of URLs a search engine will crawl on a site within a given period. It mostly matters for very large sites.

Entity: A distinct, identifiable thing (an organization, product, person or concept) that search engines and models can recognize and connect.

Featured snippet: A highlighted excerpt shown above traditional results that answers a query directly.

GEO (Generative Engine Optimization): Structuring content and managing a brand’s presence on the web so that AI answer engines (ChatGPT, Google AI Overviews and AI Mode, Gemini, Perplexity, Copilot, Claude) retrieve, cite and recommend it, and describe it correctly. Works on the brand’s own pages and on the third-party sources the engines draw on. Our guide to what a GEO agency does lists that work in detail. See generative engine optimization services.
Grounding: When an AI system retrieves live information from the web or documents to base its answer on, rather than relying only on training data.

Hallucination: An AI-generated statement that is presented confidently but is false or unsupported.
hreflang: An attribute that tells search engines which language and regional version of a page to show to which users.

Knowledge graph: A structured network of entities and the relationships between them, which search engines use to connect facts about people, organizations, places and things.

llms.txt: A proposed Markdown file at a site’s root that summarizes key content and links for large language models. Underneath publishes one; our adoption study found a valid file on 11.5% of top websites, and no evidence yet that AI systems rely on it.
LLMO (Large Language Model Optimization): An industry label for making what AI models say about a business correct and consistent. At Underneath this work is covered by generative engine optimization (GEO).
Local citation: A listing of a business’s name, address and phone number on a directory or map service. Distinct from an AI citation, which is a source link in an AI-generated answer.

People Also Ask: An expandable set of related questions and answers shown within Google search results.

Query fan-out: How an AI search system splits one question into several related sub-searches, runs them, and combines the results into one answer. Pages can be cited for a sub-search they rank for even when they do not rank for the original question.

RAG (Retrieval-Augmented Generation): A technique in which a model retrieves relevant documents before generating an answer, often with citations.

Schema markup: Structured data using the Schema.org vocabulary that describes page content in a machine-readable way.
SEO (Search Engine Optimization): Improving how a business ranks and converts in search results, including map results and AI Overviews. For how the two jobs differ, see how GEO and SEO agencies compare.

Zero-click search: A search where the user’s need is met on the results page or in an AI answer without clicking through to a website.

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