Query expansion improves search results by automatically broadening or refining the original query to include additional terms or phrases that are related to the original search intent. This can help retrieve documents that may not contain the exact query terms but are still relevant to the user's need.
For instance, if a user searches for "heart disease," a query expansion algorithm might add related terms like "cardiovascular disease," "myocardial infarction," or "heart attack" to the query. This increases the likelihood of retrieving relevant documents that use different terminologies.
Query expansion can be done in various ways, such as using synonyms, related terms, or more advanced methods like using word embeddings or analyzing the co-occurrence of terms in relevant documents. By improving the recall of the search results, query expansion helps ensure that users are exposed to a broader range of relevant content, even if their search terms are too specific or narrow.