MongoDB Atlas Search is an embedded full-text search solution that provides a seamless and scalable experience for building fast, relevance-based application features. To fine-tune the relevance of search results, developers can use function scoring to influence the order of results returned by manipulating scores based on specific criteria, such as sponsored restaurants or high-star ratings. Additionally, synonyms can be used to define terms that are semantically similar, improving search results and handling typos, especially on mobile devices.