Result sources can be used to limit the scope of searches to a certain set of content or to a particular subset of search results. Result sources may also be configured to include external search services and to send queries to third parties. Both classic and modern search experiences can use the default result source, but you can only create result sources for the classic search experience. If you change the default result source for the tenant, it will affect both classic and modern search experiences. You can use a feature called a query transform to restrict result sources to a particular subset of content as well.
You can configure a result source for the tenant, a site collection, or a site.
