Pinecone is a vector database company founded 2019, becoming the de-facto standard since the LLM RAG application explosion in 2022. Unlike traditional databases storing rows, vector DBs store high-dimensional vectors (e.g. 1536-dim OpenAI embeddings); core operation is "find the K most similar to this vector" (cosine similarity / dot product). RAG application flow: convert knowledge base text segments to embeddings stored in Pinecone → user query converted to embedding queries Pinecone for most relevant segments → inject segments into LLM context for answers. Pinecone's differentiator is "serverless UX" — unlike open-source alternatives (Qdrant, Weaviate, Milvus) requiring cluster operation, Pinecone is fully managed; developers only care about upsert and query operations. Downside: not cheap — Standard tier from $50/month, Enterprise uncapped. Open-source alternatives rising, but Pinecone still leads in enterprise RAG.