The synonym feature links two or more words which have the same meaning. For example: If a user is searching for “cheap travel” then the search results will show all the posts related to cheap travel. However you may have posts which have discounted travel in the content, this will be skipped for the “cheap travel” search. You can manually add custom synonyms, in this case “cheap,discount”. Now, for the same query, discounted travel query will also be included.