All terms

The 2026 vocabulary of Generative Engine Optimization, with live per-term citation status across ChatGPT, Perplexity, Claude, and Copilot.

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BM25
BM25 (Best Matching 25) is a probabilistic ranking function used by classical search engines and the lexical layer of modern hybrid retrieval systems. It is the standard mechanism for scoring exact-keyword match in search retrieval; its application inside specific commercial AI search engines is not vendor-documented but is consistent with observable lexical-signal behavior.
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Citation precision and recall
Citation precision is the fraction of citations in an AI engine's response that actually support the sentence they are attached to. Citation recall is the fraction of generated sentences that are fully supported by their citations. Both are model-behavior metrics, not publisher-visibility metrics: they measure how faithfully an AI engine uses the sources it cites, not how often a publisher's content appears as a source.
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Inverted index
An inverted index is the data structure classical search engines use to look up which documents contain a given term. It is the foundation under BM25 ranking and a common lexical layer in many modern hybrid retrieval systems.
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