This sort of assumes you’re familiar with vector search and vector databases. If you’re not, this might be a good place to start: https://www.pinecone.io/learn/vector-database/

TL;DR - They store vector embeddings and index them for efficient nearest-neighbor retrieval. Some also allow CRUD operations, metadata filtering, fault-tolerance, and all that jazz. Useful for things like semantic search, similarity search (of unstructured data), and recommender systems.