MotorVehicle is actually a pretty good example of the sort of class that might be abstract. You're unlikely to be interested in a generic motor vehicle. Rather you'll have trucks, motorcycles, cars, go-carts and other subclasses of MotorVehicle , but nothing that is only a MotorVehicle . An abstract method provides a declaration but no implementation. In other words, it has no method body.
Abstract methods can only exist inside abstract classes and interfaces.