This AI search glossary defines the terms marketers need to understand answer engine optimization (AEO), generative engine optimization (GEO), and how AI tools like ChatGPT, Perplexity, Gemini, and Google AI Overviews find and cite sources. Each definition is written to be short, accurate, and linked to a primary source where one exists.

AI search has created a lot of new vocabulary, and many terms overlap. Use this page as a reference, and read our complete guide to answer engine optimization to see how the pieces fit together. We update this glossary as platforms change.

Jump to: A · B · C · E · F · G · H · I · L · O · P · Q · R · S · T · Z

A

AEO (answer engine optimization)

Answer engine optimization is the practice of structuring your content, data, and brand signals so AI answer engines such as ChatGPT, Perplexity, Gemini, Microsoft Copilot, and Google AI Overviews can find your information, trust it, and cite it in their answers. Read the full answer engine optimization guide, or see how it compares with traditional SEO in AEO vs SEO.

AI crawler

An AI crawler is a bot that an AI company uses to fetch web pages, either to show them in AI search answers or to collect training data. Examples include OAI-SearchBot, GPTBot, and PerplexityBot. You control most AI crawlers through your robots.txt file.

AI Mode

AI Mode is a conversational search experience in Google Search where people ask longer questions and follow-ups and get an AI-generated answer with links to sources. Google says pages need to be indexed and eligible for a snippet to appear, with no additional requirements.

AI Overviews

AI Overviews are AI-generated summaries that appear at the top of some Google search results, with links to the web pages that support them. Being one of the linked sources is a core goal of AEO.

AI referral traffic

AI referral traffic is website traffic that arrives from links in AI tools, such as chatgpt.com, perplexity.ai, gemini.google.com, and copilot.microsoft.com. You can see it in GA4 by filtering session source for those domains or by building a custom channel group.

AI visibility

AI visibility describes how often and how favorably your brand appears in AI-generated answers for the questions your buyers ask. It is usually measured with citation frequency, brand mention rate, and share of voice across a fixed set of prompts.

Answer engine

An answer engine is a search product that responds to a question with a written answer instead of, or on top of, a list of links. ChatGPT search, Perplexity, Gemini, Microsoft Copilot, and Google AI Overviews are all answer engines.

Answer-first content

Answer-first content opens each section with a direct answer to the question in its heading, usually in 40 to 60 words, before adding detail. It gives readers and AI systems a clean passage to quote. It is also called the BLUF method.

B

BLUF (bottom line up front)

BLUF stands for bottom line up front, a writing method that puts the main point or answer first. In AEO, it means opening each section with the direct answer so an AI system can lift it without reading the whole page.

Brand mention

A brand mention is any time your brand is named, with or without a link. In AI search, a mention means the answer names your brand, even if it doesn’t link to your site. Unlinked mentions on trusted sites also help models associate your brand with your category.

C

ChatGPT search is the feature that lets ChatGPT retrieve current web results and cite them with links. OpenAI introduced it in October 2024 and says it uses third-party search providers along with content from partners. Sites that block OAI-SearchBot won’t appear in its answers.

Citation

In AI search, a citation is a link to a source page that an AI answer shows to support what it says. A citation can send traffic and signals that the engine treated your page as a trusted source.

Citation frequency

Citation frequency is how often AI answers link to your pages across a fixed set of tracked prompts and engines. It is one of the main AEO metrics, alongside brand mention rate and share of voice.

Co-occurrence

Co-occurrence is when your brand name appears near a topic or category on the same pages across the web. Language models learn associations from text, so frequent co-occurrence on trusted sites helps a model connect your brand with the topics you want to be known for.

Core Web Vitals

Core Web Vitals are Google’s metrics for page experience: Largest Contentful Paint (loading), Interaction to Next Paint (responsiveness), and Cumulative Layout Shift (visual stability). Google recommends an Interaction to Next Paint of less than 200 milliseconds.

E

E-E-A-T

E-E-A-T stands for experience, expertise, authoritativeness, and trustworthiness. Google says E-E-A-T itself isn’t a specific ranking factor, but its systems use a mix of signals to reward content that demonstrates it. Named authors, credentials, and cited sources help.

Entity

An entity is a distinct thing that search engines and AI models can identify, such as a company, person, product, or place. Keeping your company’s name, description, and details consistent across the web makes it easier for AI systems to recognize your brand as one entity.

F

A featured snippet is a highlighted excerpt from a web page that Google shows near the top of some search results to answer a question directly. The same answer-first formatting that wins featured snippets also helps content get quoted in AI answers.

G

Generative engine optimization (GEO)

Generative engine optimization is another name for optimizing content to appear in AI-generated answers. The term was introduced in a 2023 research paper presented at KDD 2024, which found that adding quotations, statistics, and citations could boost visibility in AI answers by up to 40%.

Google-Extended

Google-Extended is a robots.txt token that lets site owners control whether Google uses their content to train Gemini models and to ground Gemini Apps and Vertex AI responses. Google says it does not affect inclusion or ranking in Google Search.

GPTBot

GPTBot is OpenAI’s crawler for collecting content that may be used to train its AI models. Blocking it signals that your content should not be used for training. It does not control whether you appear in ChatGPT search; OAI-SearchBot does.

Grounding

Grounding is when an AI system bases its answer on specific sources, such as live search results or documents, instead of only on what it learned in training. Grounded answers usually include citations, which is where AEO creates visibility.

H

Hallucination

A hallucination is a confident but false statement produced by an AI model. Clear, consistent, well-sourced information about your brand reduces the chance that AI answers describe it inaccurately.

I

Indexing

Indexing is when a search engine stores a page so it can appear in results. Google says a page must be indexed and eligible for a snippet to appear in AI Overviews and AI Mode, so indexing is the starting point for AEO.

IndexNow

IndexNow is a protocol that lets websites notify participating search engines when pages are added, updated, or deleted. Participating engines include Microsoft Bing, Naver, Seznam.cz, Yandex, and Yep.

Information gain

Information gain is the new information a page adds beyond what other pages on the topic already say, such as original data, expert quotes, or first-hand examples. AI systems have already seen the common version of most topics, so information gain makes a page worth citing.

L

Large language model (LLM)

A large language model is an AI model trained on large amounts of text to understand and generate language. ChatGPT, Gemini, Claude, and the models behind Perplexity and Copilot are built on LLMs.

LLM SEO

LLM SEO is optimization aimed at getting content and brands cited by AI systems built on large language models. It is another name for answer engine optimization and GEO.

llms.txt

llms.txt is a proposed Markdown file at a site’s root that gives language models a curated summary of the site’s key pages. Jeremy Howard of Answer.AI proposed it in September 2024. It is optional, and major AI search providers have not confirmed they rely on it.

O

OAI-SearchBot

OAI-SearchBot is OpenAI’s crawler for ChatGPT search. OpenAI’s documentation says sites that block it will not be shown in ChatGPT search answers, although they can still appear as plain navigational links.

P

Parametric knowledge

Parametric knowledge is what an AI model learned during training and stores in its internal weights. When a model answers without searching, it relies on parametric knowledge, which is why a consistent brand presence across the web matters over time.

PerplexityBot

PerplexityBot is the crawler Perplexity uses to surface and link websites in its search results. Perplexity says it is not used to crawl content for AI foundation models and recommends allowing it in robots.txt.

Prompt

A prompt is the question or instruction a person types into an AI tool. Prompts tend to be longer and more specific than search keywords, so AEO research focuses on the full questions buyers ask.

Prompt tracking

Prompt tracking is running a fixed list of buyer questions through AI engines on a regular schedule and recording whether your brand is mentioned or cited, how it is described, and which competitors appear. It can be done by hand or with an AI visibility tool.

Q

Query fan-out

Query fan-out is a technique Google uses in AI Overviews and AI Mode, issuing multiple related searches across subtopics and data sources to build one answer. It means a page can be cited for a sub-question even if it doesn’t rank for the main query.

R

Retrieval-augmented generation (RAG)

Retrieval-augmented generation is an approach where an AI system retrieves relevant documents first and then writes an answer grounded in them. It was formalized in a 2020 paper by Lewis and colleagues and underpins most AI search products.

robots.txt

robots.txt is a text file at the root of a website that tells crawlers which parts of the site they may access. For AEO, check that it allows search crawlers such as Googlebot, Bingbot, OAI-SearchBot, and PerplexityBot.

S

Schema markup

Schema markup, also called structured data, is code that describes a page’s content in a standard format from Schema.org, such as Organization, Article, or FAQPage. Google asks that structured data match the visible content on the page.

Share of voice

In AI search, share of voice is your brand’s share of mentions or citations compared with competitors across the same set of prompts. It shows whether you are gaining or losing ground in AI answers, not just whether you appear.

Snippet controls

Snippet controls are the nosnippet, data-nosnippet, max-snippet, and noindex directives that limit what Google can show from a page. Google says these controls also limit what appears in its AI features, so check that none are set by accident.

T

Training data

Training data is the text and other content used to build an AI model before it is released. Training crawlers such as GPTBot collect it. Being represented accurately in training data shapes what a model knows about your brand when it answers without searching.

Z

A zero-click search is one where the person gets their answer on the results page and doesn’t click through to a website. A Pew Research Center study found users clicked a traditional result in 8% of visits when a Google AI summary appeared, compared with 15% when it didn’t.

Put these terms to work

Knowing the vocabulary is the first step. Sentic is a national digital marketing agency specializing in AI search optimization, SEO, paid search, paid and organic social, and websites. Our answer engine optimization services track how your brand appears across AI engines and fix what keeps you out of the answers. Request a free growth audit to see where you stand today.