I hear the whole day the terms class library, base class library, Framework, ...
What highlights a framework and what a base class library?
The distinguishing feature between a class library and a software framework is that in a framework, the flow of control is not determined by the user´s code, but by the framework.
This is also known as Hollywood principle (don´t call us, we call you).
By the way, there is also a nice Wikipedia article on this topic.