Term
Hybrid Search
Hybrid search combines lexical full-text search (e.g. BM25) with semantic vector search and unites the strengths of both — precise on keywords and robust on meaning.
Hybrid Search — explained
Pure vector search struggles with rare proper nouns, product codes, or typos — terms that barely appear in the training corpus have no meaningful semantic neighborhood. Pure full-text search, on the other hand, fails on synonyms and paraphrases. Hybrid search runs both methods in parallel and fuses the result lists — usually via Reciprocal Rank Fusion (RRF) or a linear score combination. The end result is noticeably more robust than either retriever alone.
Example / Practical context
A support bot needs to answer both “How do I reset my password?” and “Error message E_AUTH_402” with good hits. Vector search dominates the first (natural language question), BM25 the second (exact code). Hybrid search produces usable top results for both. Vector DBs like Qdrant, Weaviate, Pinecone, and Postgres with pgvector + tsvector support hybrid setups out of the box.
Distinction from related terms
Hybrid search is a retrieval strategy, not its own algorithm — the building blocks are still classic BM25 and vector indexes. Reranking is the step that often follows: a cross-encoder reorders the fused top-N more precisely. Multi-query and query expansion modify the query itself, instead of combining two retrievers.
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GlossarS-RAG
S-RAG (Search-optimized RAG) is boostN.ai's take on Retrieval-Augmented Generation. It extends classic RAG with search-engine principles: relevance ranking, recency decay and typed links between chunks for deterministic follow-up retrieval.
LexikonRAG Tuning and Balancing — Embeddings, Weights, Decay and MCP for Advanced Setups
How to steer retrieval on purpose: embedding choice, hybrid weights, reranker cascades, time decay, authority boost, MMR and MCP as a retrieval tool.