Search abandonment is the share of searches after which the visitor clicks nothing, refines nothing and converts on nothing. It is a better health metric than zero-result rate because it also captures the more common failure: results were returned, and none of them were right.
Abandonment rate is searches with no subsequent meaningful action divided by total searches. Segment by query rather than reading the aggregate — abandonment concentrates in a small number of recurring query shapes, and the average hides exactly the queries you need to fix.
A searcher has already declared intent. They arrived, decided what they wanted, and told you in their own words. Losing them is losing a visitor much further down the funnel than an average browser — which is why search abandonment is disproportionately expensive relative to its volume.
Relevant results ranked below the fold, no filters to narrow a large set, results that ignore an explicit constraint in the query, out-of-stock items occupying the top rows, and non-product questions receiving product grids.