An integration test is something that tests a functionality that is dependant on an external system e.g. a database, HTTP API, or message queue.
Integration vs Unit Tests
The line is thin in my opinion. The integration part can be faked, or embedded services can be used in place of the actual integration point, and with these solutions, the interaction with the external system is bounded in the test context and the tests can be executed in isolation so they are very much like unit tests.