ModelRefs / Hybrid Search — AI Glossary
Hybrid Search — AI Glossary
A retrieval strategy that fuses lexical (BM25 keyword) and semantic (vector embedding) signals for better recall.
Overview
Hybrid search recovers exact-match recall that pure vector search misses (product codes, names, rare terms) while keeping semantic generalization for paraphrase. Reciprocal Rank Fusion (RRF) is the most common fusion method.
Reference details
| Topic | rag |
|---|---|
| Last reviewed | 2026-06-24 |
Related terms
Example: The query each half gets wrong
Search “ORA-01555 snapshot too old”. Dense retrieval embeds it near general database-error text and may return the wrong code. BM25 matches the literal string and nails it. Now search “why does my long-running report keep failing” — BM25 finds nothing useful because the document never uses those words, and dense retrieval finds it immediately. Hybrid runs both and fuses the rankings, which is why production retrieval rarely picks a side.
Commonly confused with
Hybrid search is not simply running two searches and concatenating results. The fusion step is the substance: two rankings with incomparable score scales have to be combined into one order. Reciprocal Rank Fusion is common precisely because it uses rank position and ignores the raw scores, which are not on the same scale.
When to use it
Reach for it when:
- Queries mix natural language with identifiers, codes or product names
- Either method alone shows recall gaps you can point at in evaluation
- You can afford two index lookups per query
Reach for something else when:
- Queries are uniformly one kind — all lexical or all conversational
- You have not measured which half is failing; hybrid can mask a fixable retriever
- Latency budget will not absorb a second search plus fusion
Referenced by
This term is used by the following ModelRefs references:
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Frequently asked questions
What is Hybrid Search?
A retrieval strategy that fuses lexical (BM25 keyword) and semantic (vector embedding) signals for better recall.
What concepts are related to Hybrid Search?
Closely related concepts include bm25, semantic search, reranker, reciprocal rank fusion.