Use result sources to scope search results and federate queries to external sources, such as internet search engines. After ...

Use result sources to scope search results and federate queries to external sources, such as internet search engines. After defining a result source, configure search web parts and query rule actions to use it. Learn more about result sources. 
Result Sources replace Search Scopes, which are now deprecated. You can still view your old scopes and use them in queries, but not edit them.