Query expansion improves search results by enriching the user's original query with synonyms, related terms, or reformulations before retrieval. If a customer types «cheap riad Marrakech», the system may also search for «affordable guesthouse Marrakesh» to catch documents phrased differently. In RAG pipelines, a language model often generates several variants of the question so the retriever finds more relevant passages. It is a low-cost technique that noticeably boosts recall.