What is a vector database and which one should I use?

A vector database stores and indexes embeddings for fast approximate-nearest-neighbour (ANN) search. Popular options: Pinecone (managed, easy), Weaviate (open-source, feature-rich), Qdrant (Rust-based, fast), pgvector (PostgreSQL extension — best if you’re already on Postgres). For prototyping, even FAISS in memory works.