Reranking
A second scoring pass applied to a small set of retrieved candidates, using a model that reads the query and passage together rather than comparing precomputed vectors. It is slower per pair than retrieval-augmented generation's first-stage lookup, which is exactly why it only runs on a shortlist rather than the whole index.
Why exams ask this
Tested as the fix for "retrieval returned the right passage at rank six instead of rank one." A reranker is a second, slower, more accurate pass over a small candidate set, not a replacement for the first-stage retriever. The distractor proposes retrieving more candidates instead of scoring them better.
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