Glossary

Key terms and definitions

A

AEO: Answer Engine Optimization: the practice of structuring content to be selected and cited by AI-powered answer surfaces, including Google AI Overviews, Perplexity, and ChatGPT Search. Distinct from traditional organic rank optimization.
AI Mode: Google's full conversational search interface powered by Gemini, expanding via Labs opt-in as of 2026. Unlike AI Overviews, AI Mode returns no organic results list; sources are selected via up to 16 simultaneous sub-queries and sites are either cited or absent with no fallback organic position.
AI Overview (AIO): A generative AI-produced summary that appears at the top of certain Google Search results pages, drawing from multiple sources to answer a query directly. Introduced broadly in 2024 and now present across a significant share of informational queries.
AI Overviews: Google's AI-generated summary responses that appear above organic search results for informational queries. AI Overviews cite sources inline; appearing in them is distinct from ranking in organic results and is tracked separately in Google Search Console.
Answer Engine Optimization: Abbreviated AEO. The practice of optimizing content to appear as cited sources in AI-generated answers from platforms including Google AI Overviews, AI Mode, Perplexity, and ChatGPT Search. Distinct from traditional SEO in that citation selection signals differ by platform and are not fully documented by any provider.

Citation Share: The proportion of AI Overview appearances for a given query set in which a site's pages are cited as sources. A separate metric from organic market share or ranking position; citation share can move independently of rank.
Citation signal: A structural or content feature correlated with a page being cited as a source within an AI-generated answer. FAQ schema is hypothesized to function as one such signal based on correlation data from Search Engine Land.

Difference-in-differences: A statistical method that estimates the causal effect of a treatment by comparing the change in outcomes for a treated group against the change in outcomes for a control group over the same period. Used in the Ahrefs schema study to isolate whether adding schema markup caused AI citation changes, not merely correlated with them.

FAQPage schema: A schema.org structured data type that marks up question-and-answer content on a web page. Originally used to generate FAQ rich results in Google Search; now functions as a structured inference signal for AI platforms including Google AI Overviews.

JSON-LD: JavaScript Object Notation for Linked Data; a structured data format used to embed machine-readable schema markup in a web page's HTML head without altering visible content. Commonly used to implement Schema.org types for search engines.

Query Fan-Out: A mechanism used by Gemini-powered AI Overviews in which a single user query is decomposed into multiple related sub-queries, each evaluated independently for the most relevant source. This process decouples source selection from ranking position on the original query.

Randomized controlled experiment: A study design in which participants are randomly assigned to treatment and control groups, allowing researchers to attribute observed differences to the treatment rather than to confounding variables.
Rich results: Enhanced search result displays generated from structured data markup on a page. Examples include FAQ accordions, review stars, and how-to steps. Google's FAQ rich results were deprecated on May 7, 2026.

The Great Decoupling: A term coined by Ahrefs in June 2025 to describe the reversal of the impressions-to-clicks correlation from +0.425 in late 2024 to -0.352 in early 2025, driven by the expansion of AI Overviews reducing click-through rates even as impressions grew.

Zero-click search: A search session that ends without the user clicking through to any external website; the user's need is satisfied or abandoned within the results page itself.