Defined terms

Glossary

The vocabulary of AI search, 44 terms deep. Each entry is a self-contained definition plus enough context to ground further reading, cross-linked to the related terms and guides, with a stable canonical URL so AI engines can cite it.

• GEO (Generative Engine Optimization)

  Generative Engine Optimization · AI search optimization

  The discipline of getting your content picked up, grounded against, and cited by generative AI search engines like ChatGPT Search, Perplexity, Claude, Gemini, and Google AI Overviews.

• AEO (Answer Engine Optimization)

  Answer Engine Optimization

  The discipline of structuring content so answer engines (Google AI Overviews, featured snippets, People Also Ask, voice assistants) extract your page as the direct answer. The older sibling of GEO; the two converge but are not synonyms.

• RAG (Retrieval-Augmented Generation)

  Retrieval-Augmented Generation

  The architecture pattern where an AI engine retrieves source documents from a corpus before generating an answer, conditioning the response on the retrieved context. The technical foundation underneath both AEO and GEO.

• AIO (AI Overviews / AI Optimization)

  AI Overviews · AI Optimization

  Two distinct meanings sharing the same acronym. Most often refers to Google's AI Overviews: the SERP-integrated AI answer block. Sometimes used as a catch-all for AI Optimization across all engines (a near-synonym for GEO + AEO).

• llms-full.txt

  llms-full

  A companion to llms.txt that contains the full Markdown content of a site's priority pages concatenated into a single file, intended for AI engines that prefer single-fetch corpus ingestion.

• Citation share

  AI citation share · share of voice (AI)

  The GEO equivalent of organic share of voice: the percentage of AI engine answers in a query set that cite your domain. The primary KPI for measuring AI visibility programs.

• Grounding model

  retrieval model · grounding pipeline

  The specific architecture an AI engine uses to retrieve and condition its answer on external sources. Differs meaningfully across engines and is the variable that determines which content gets cited.

• Schema.org for AEO and GEO

  AEO schema · AI search schema

  The subset of Schema.org structured data types that AI engines (both extractive AEO and generative GEO) prioritize for grounding signals. Not every schema type carries equal weight.

• Attribution (AI engine)

  AI attribution · source attribution

  How an AI engine credits the sources that contributed to its answer, including but broader than citation. Covers inline citations, side panels, mouseover sources, hidden provenance metadata, and the entity disambiguation that decides who gets credit at all.

• llms.txt

  llms-full.txt

  A proposed text file at /llms.txt that gives AI engines a curated, structured map of a site's most-citable content: the LLM-era equivalent of robots.txt or sitemap.xml.

• Grounding

  RAG · Retrieval-Augmented Generation

  The retrieval step that ties an LLM's answer to specific, citable source documents, distinguishing AI search from generative chat that hallucinates.

• Citation (AI engine)

  AI citation · AI source attribution

  A linked source shown in an AI engine's answer, attributing a claim to the page it was grounded from. The new ranking signal of AI search.

• SEO (Search Engine Optimization)

  Search Engine Optimization · organic search optimization

  The discipline of getting pages to rank in the organic (unpaid) results of search engines, historically Google, increasingly also Bing as it powers AI engines. The parent practice from which AEO, GEO, AIO, and LLMO all branch.

• SEM (Search Engine Marketing)

  Search Engine Marketing · paid search

  The umbrella for paid search advertising (Google Ads, Bing Ads, search-network campaigns) and, in some usages, all search-channel marketing including organic SEO. In current practice usually means the paid side specifically.

• SERP (Search Engine Results Page)

  Search Engine Results Page

  The page a search engine returns for a query: historically a ranked list of blue links, now an assembled experience with AI Overviews, featured snippets, People Also Ask, knowledge panels, ads, and organic results all sharing the screen.

• LLMO (Large Language Model Optimization)

  Large Language Model Optimization · LLM optimization

  An umbrella term for optimising content so large language models (both grounded AI search engines and the underlying LLMs they're built on) surface, quote, and cite it. In practice a near-synonym for GEO with a slightly different framing.

• E-E-A-T (Experience, Expertise, Authoritativeness, Trustworthiness)

  EEAT · E-A-T · Experience Expertise Authoritativeness Trustworthiness

  Google's quality framework (originally E-A-T, expanded in December 2022 to add Experience) that quality raters use to evaluate content and that the ranking systems are tuned against. The trust framework AI engines increasingly mirror.

• Featured snippet

  position zero · answer box

  A SERP feature that lifts a short passage from a ranking page and displays it directly as the answer to a query, with the source linked beneath. The original AEO target and still a meaningful traffic surface in 2026.

• People Also Ask (PAA)

  PAA · Related questions

  A SERP feature showing expandable related questions beneath the initial result, each revealing an extracted answer when clicked. A high-volume AEO surface that's easier to win than featured snippets.

• Knowledge graph

  knowledge panel · entity graph

  Google's (and other engines') structured entity database (people, organisations, products, places) that powers knowledge panels, entity disambiguation, and increasingly AI engine grounding. Being a recognised entity in the knowledge graph is foundational for AI search visibility.

• Zero-click search

  zero-click · no-click search

  A search that ends without the user clicking through to any organic or paid result: the query is answered within the SERP itself by an AI Overview, featured snippet, knowledge panel, or other extracted surface. The dominant SERP behaviour for informational queries in 2026.

• Answer engine

  AI answer engine

  A search system that returns an assembled answer rather than a ranked list of links. The category includes ChatGPT Search, Perplexity, Claude, Gemini, Google AI Overviews, and Bing Copilot. The noun that gives Answer Engine Optimization its name.

• LLM (Large Language Model)

  Large Language Model · foundation model

  A neural network trained on a large text corpus to predict and generate language. The underlying model class behind ChatGPT, Claude, Gemini, and every other generative AI engine: the L in LLMO and the engine doing the work in every answer engine.

• Semantic search

  meaning-based search · neural search

  Search that matches the meaning of a query against the meaning of documents (using vector embeddings) rather than matching keyword tokens. The retrieval layer underneath every modern AI search engine.

• Vector search

  embedding search · dense retrieval

  Retrieval that compares the vector embeddings of a query and candidate documents, returning documents whose embedding is most similar to the query's. The mechanical core of semantic search and RAG.

• Entity SEO

  entity-based SEO · entity-first SEO

  An SEO discipline that optimises for engine recognition of entities (people, organisations, products, concepts) rather than keyword rankings. The framing that maps most directly onto how AI engines decide who to cite.

• Topical authority

  topic authority · subject-matter authority

  The signal that an organisation or author is the recognised expert on a specific topic, built through comprehensive coverage, consistent expertise signals, and internal linking that demonstrates topical depth. The engine-visible cousin of E-E-A-T.

• AI crawler

  AI bot · LLM crawler · GPTBot · ClaudeBot · PerplexityBot

  A web crawler operated by an AI engine or LLM provider, used to build training corpora and retrieval indexes. The bots whose access controls determine whether your content is reachable to AI engines at all.

• Query fan-out

  fan-out queries · query expansion

  An AI search behaviour where the engine generates multiple related sub-queries from a single user question and retrieves sources for each, then synthesises the answer across all of them. The mechanism that made Google's AI Mode notably different from classical search.

• Hallucination

  AI hallucination · confabulation

  An LLM generating content that sounds plausible but is factually wrong, unsupported by its sources, or fabricated. The reliability risk that grounding and citation requirements partly mitigate, and the publisher behaviour that reduces being misattributed.

• PLG (Product-Led Growth)

  Product-Led Growth · product-led

  A go-to-market motion where the product itself drives acquisition, conversion, and expansion through self-serve signup, free tiers, and documentation-first content. Structurally advantaged in AI search because the artifacts it produces are exactly what engines prefer to ground against.

• Share of voice (AI search)

  AI share of voice · SOV

  A competitive framing of citation share: across a query set, how much of the total AI-engine citation goes to your domain versus named competitors. The metric that maps AI visibility onto the competitive language marketing teams already use.

• Brand mention (unlinked citation)

  unlinked mention · unlinked citation

  When an AI engine names your brand in an answer without a clickable link. A first-class AI-search KPI in its own right, because the model can recommend you without sending a citation chip, and the recommendation still shapes the buyer.

• Agentic search

  AI agents · agentic retrieval · deep research

  AI search that runs multi-step, autonomous retrieval: the model plans sub-questions, retrieves, evaluates what it found, and iterates before answering. The mode behind 'deep research' and 'DeepSearch' features, and the one that rewards topical depth most heavily.

• Conversational search

  multi-turn search · chat search

  Search conducted as a multi-turn dialogue, where the user refines and drills down within a session and the engine preserves context across turns. The interaction model of every answer engine, and the reason single-keyword optimization no longer fits.

• Chunking

  passage chunking · content chunking

  The step where a retrieval system splits documents into smaller passages (paragraphs or token windows) before embedding and indexing them. The reason a single self-contained paragraph retrieves better than the same idea spread across a page.

• Digital PR (for AI visibility)

  earned media · digital public relations

  Earning mentions, citations, and coverage on authoritative third-party sites to build the entity and trust signals AI engines weight. The off-page half of AI visibility, and increasingly the harder half to fake.

• AI Search Optimization (AISO / GAIO / SXO)

  AISO · GAIO · SXO · AI Search Optimization · Generative AI Optimization

  The cluster of competing umbrella acronyms (AISO, GAIO, SXO, and others) that all mean roughly 'optimizing to be visible in AI search.' Near-synonyms for the GEO-plus-AEO whole, differing more in who coined them than in what they describe.

• MCP (Model Context Protocol)

  Model Context Protocol

  An open standard (introduced by Anthropic in late 2024) for connecting AI models to external tools and data sources through a common interface. Relevant to AI search as the plumbing that lets agents fetch, query, and act on content rather than only reading crawled pages.

• Passage ranking

  passage indexing · passage retrieval

  Ranking and retrieving individual passages of a page rather than the page as a whole, so a single strong section can surface even when the overall page is not the best match. The retrieval behavior that makes paragraph-level quality decisive for AI search.

• Content half-life (freshness decay)

  content decay · freshness decay · content half life

  The rate at which a page loses AI-search visibility as it ages and its dating signals go stale. AI engines weight recency heavily, so undated or visibly-old content is discounted relative to fresh equivalents, faster in fast-moving topics.

• Citation panel (sources panel)

  sources panel · sources carousel · source cards

  The user-visible UI element where an answer engine shows the sources it grounded against: a numbered footnote list, a sidebar of source cards, or a horizontal carousel. The surface where a citation becomes a click, and where citation position drives click-through.

• Machine-readable content

  machine-readable · AI-readable content

  Content structured so that machines (crawlers, retrievers, and LLMs) can parse, extract, and attribute it cleanly: semantic HTML, structured data, clean text rendering, and dedicated AI-facing files. The structural half of AI-search optimization, distinct from the editorial half.

• robots.txt (for AI crawlers)

  robots exclusion · robots file

  The text file at /robots.txt that tells crawlers which paths they may fetch. In the AI era it is the lever publishers use to allow or block AI crawlers per user agent, with the crucial caveat that it is honor-system, not enforcement.