Reranking
also: cross-encoder
A second, smarter pass that reorders retrieved candidates before they reach the prompt.
First-stage retrieval optimizes recall over millions of documents; reranking optimizes precision over the top ~100. A cross-encoder reads query and document together — far more accurate than comparing separate embeddings, far too slow to run over everything. The retrieve-then-rerank cascade is the standard two-stage design, and often the single biggest RAG quality upgrade.