In CeePlusPlus, a class that has any PureVirtual member functions is an abstract base class.
seems to suggest that, at least for C++, an abstract base class is the same as an abstract class.
However, I still think it's clear that while all Moose roles are abstract classes (they cannot be instantiated), only those Moose roles which do nothing more than list 'requires' are abstract base classes. None of the Moose roles I am using are abstract base classes.
Having read more about the "interface role", I've changed my mind. What I called an abstract base class above is really an interface-only role. Arunbear recognized this in the beginning. I don't have any of these in my real code.