Hypothetical Document Embeddings (HyDE) is a Zero-Shot retrieval enhancement technique that bridges semantic distribution gaps between short queries and long documents; given user query
q, HyDE prompts an offline LLM to synthesize a 'Hypothetical Document'
dhypo; even if factually ungrounded, its vocabulary distribution and syntactic domain align closely with true target documents;
dhypo is then embedded into the vector store, converting asymmetric 'query-to-doc' search into symmetrical 'doc-to-doc' retrieval.