Sitecore Search is a search and discovery product. It indexes content from your sites and other sources and returns fast, relevant results through APIs and widgets. It can power site search, product discovery and content recommendations from one platform, which keeps the experience consistent.
Teams can tune results, set up filters and recommendations, and review search analytics. It suits sites with large amounts of content, such as product catalogues or knowledge bases.
Search is included at entry level in SitecoreAI.
If you are weighing search options, read Coveo or Sitecore Search.