What is the difference between naive RAG, advanced RAG, and modular RAG?

Naive RAG is the basic pattern: chunk, embed, retrieve top-k, stuff into prompt, generate. Advanced RAG adds optimizations like query rewriting, hybrid search, reranking, and metadata filtering to improve retrieval precision. Modular RAG goes further by treating each stage as a swappable module, supporting patterns like multi-query retrieval, self-query routing, agentic RAG with tool use, and iterative retrieval where the model decides what to fetch next. The taxonomy comes from a 2023 survey by Gao and colleagues categorizing the evolution of RAG systems.