Glossary · Retrieval & generation

Approximate Nearest Neighbor (ANN)

A search method that returns vectors likely to be among the nearest to a query without exhaustively comparing the query with every stored vector.

Why it matters

Approximation makes large vector indexes practical, but it introduces a measurable tradeoff between search speed, memory, and retrieval recall.

In practice

Tune index and search parameters against a held-out query set, then report latency together with Recall@K instead of assuming every true neighbor is found.

Common confusion

ANN describes a search objective and tradeoff, while HNSW is one particular index algorithm that can implement it.

Related terms

Vector Database
HNSW
Cosine Similarity
Recall@K

Sources

Efficient and Robust Approximate Nearest Neighbor Search Using HNSW

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