Query Expansion
A retrieval technique that adds synonyms, related expressions, or feedback-derived terms to a user's query in order to improve recall.
Short queries often compress an intent into one or two words. Query expansion can recover alternate terminology and improve recall, but an incorrect expansion can destroy precision just as quickly.
The trade-off is sharper in technical search. Product names, protocol acronyms, and error codes may be harmed by semantically broad substitutions. When lexical BM25 and dense retrieval coexist, the stage at which expansion is applied becomes an architectural decision rather than a text-preprocessing detail.