Definition
Impression share is the portion of available appearances a brand captures for a given set of queries, measured against the total it could have captured. Where a raw count says how often a brand showed up, impression share says how often it showed up out of every time it could have. It measures presence against a ceiling rather than in isolation.Why It Matters for AI Search
In answer engines the ceiling is different from the one search advertising defined. A generated answer names a handful of sources, not a page of ten blue links, so the available appearances for any query are few and the competition for them is sharp. Reading visibility as a share of that scarce space, rather than as a total, is what makes it comparable across queries and over time. Share of model applies the same logic to how often a brand is the one a system reaches for, and both reframe visibility as a contest for limited room rather than a tally.Related Terms
Share of model
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SERP
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Featured snippet
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Brand authority
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