What is hybrid search and why is it often better than pure vector search?

Hybrid search combines lexical search (BM25/keyword) with vector (semantic) search, then merges the results. Vector search captures meaning but can miss exact tokens — part numbers, error codes, names, rare terms — while keyword search nails those but misses paraphrases. Combining them, often with a reranker on the merged candidates, consistently beats either alone on production QA corpora. It's a common answer to 'my RAG misses obvious exact-match results'.