Linq is really just a high level abstraction for querying any data that can be queried. EF adds some more abstractions mostly related to mapping C# objects to database tables. Then it adds database specific query providers (implementations) that combine the (abstract) linq query and the mapping to produce sql.

You can really use linq to query anything (APIs, for example), including databases without using EF. It's just not very common because building a custom query provider is a lot of work.

Linq2SQL was a thing. I’m not even sure if it is still supported.