Exactly what is integration testing - compared with unit

Question

I am starting to use unit testing in my projects, and am writing tests that are testing at the method/function level.

I understand this and it makes sense.

But,

Answer 1

Consider a method like this PerformPayment(double amount, PaymentService service);

An unit test would be a test where you create a mock for the service argument.

An integration test would be a test where you use an actual external service so that you test if that service responds correctly to your input data.