The term business logic is in my opinion not a precise definition. Evans talks in his book, Domain Driven Design, about two types of business logic:
This separation is in my opinion a lot clearer. And with the realization that there are different types of business rules also comes the realization that they don't all necessarily go the same place.
Domain logic is logic that corresponds to the actual domain. So if you are creating an accounting application, then domain rules would be rules regarding accounts, postings, taxation, etc. In an agile software planning tool, the rules would be stuff like calculating release dates based on velocity and story points in the backlog, etc.
For both these types of application, CSV import/export could be relevant, but the rules of CSV import/export has nothing to do with the actual domain. This kind of logic is application logic.
Domain logic most certainly goes into the model layer. The model would also correspond to the domain layer in DDD.
Application logic however does not necessarily have to be placed in the model layer. That could be placed in the controllers directly, or you could create a separate application layer hosting those rules. What is most logical in this case would depend on the actual application.