Amazon's own ranking of how important a given search term is to a product, blending search volume and relevance into a single number — lower is better.
Because purchases are "a big part of how Amazon actually determines the score," the Search Query Score closely tracks a term's rank when the Amazon Search Query Performance (SQP) Report is sorted by brand purchase count. In practice, sellers skip the score itself and sort directly by purchases, since purchases are "the data that we really trust" and effectively reproduce Amazon's own prioritization without needing a separate column.
Use it as a rough sanity check on term importance, not as the primary sort key.