It's a way of giving LLMs extra information (usually fast changing) that they were no trained with so that you can have them return relevant information. Think

It's a way of giving LLMs extra information (usually fast changing) that they were no trained with so that you can have them return relevant information. Think of asking an LLM "Who is Paul Graham" (assuming PG is relatively unknown) and it would say it doesn't know. But if you search your own knowledge base and then augment the prompt to something like "Paul Graham is a well known Venture Capitalist. Who is Paul Graham?", it can give you that information back. The idea of adding the extra information is the augmenting and you do that by retrieving relevant information from a knowledge base before you involve the LLM.