Definition
Citation share is the AEO-era equivalent of market share: of all the AI answers an engine generates for prompts in your category, what percentage cite your domain? It's measured per-engine (ChatGPT vs Perplexity vs Gemini may show different shares) and per-prompt-set (a portfolio of buyer queries).
For the prompt 'best CRM for small agencies', if Perplexity cites HubSpot 35% of the time, Salesforce 25%, Pipedrive 20%, and yours 5%, your citation share for that prompt is 5%.
How to optimize
Track citation share across a portfolio of 20-50 buyer queries. Identify which competitors lead which prompts. For each leading competitor, audit their on-page signals (EEAT, schema, BLUF). Close gaps with VectorCite's Fix Kit.