Here:
https://blogs.nvidia.com/blog/what-is-retrieval-augmented-ge...
RAG is training AI to be a guy who read a lot of books. He doesn't know all of them in the context of this conversation you are having with him, but he sort of remembers where he read about the thing you are talking about and he has a library behind him into which he can reach and cite what he read verbatim thus introducing it into the context of your conversation.
I might be wrong though. I'm a newb.
> Retrieval Augmented Generation (RAG) is a technique where the capabilities of a large language model (LLM) are augmented by retrieving information from other systems and inserting them into the LLM’s context window via a prompt.
(stolen from: https://github.com/psychic-api/rag-stack)