Definition
Plain language
Fast lookup that finds something close to what you're looking for, trading exactness for speed.
As stated in the literature
A family of indexing algorithms that retrieve approximately closest vectors under a distance metric, used in vector databases and semantic search.
Also called: ANN, nearest neighbor
Why it matters: Exact nearest-neighbor search doesn't scale, and almost every retrieval-augmented AI system depends on this approximation to be fast enough to deploy.
For example, a vector database uses approximate nearest neighbor search to fetch the dozen most similar documents to your query in milliseconds, even from a billion-document corpus.
Heard on the show
“On the looks map, what's its nearest neighbor — the concept whose drawings look most like it?”Episode 209 — How 2.6 Billion Doodles Exposed the Culture Words Quietly Delete