The search platform that operates within SharePoint.
This high-level overview of how search works can help you understand where and how you can customize the search in SharePoint Online.
In lists and libraries, site columns store detailed information about each document.
Search crawls the lists and libraries and adds the site columns and values to the search index.
In the search index, site columns are mapped to managed properties.
When a user enters a query in a Search Box Web Part, the query is sent to the search index.
The search engine finds matching results and sends them to a search results page where the results are displayed in Web Parts.
You can read more about search in sharepoint, here.
Any questions relating to search, either performing queries or indexing, should use this tag.