FUP means Fair Use Policy
A FUP often applies when using an Internet connection. You may download it, but it should not be done constantly so that other users are bothered by it: it is therefore not allowed to be extremely much data user. What happens when the FUP is violated varies by contract, it may be that no data traffic is possible at all, or that an additional account is coming. Because Fair Use is rather opaque, you don't know as a user when you are violating it.