In the Unified Modeling Language 1.x, powertype is a keyword for a specific UML stereotype, and applies to a class or dependency. Powertype shows a classifier whose instances (objects) are children of the given parent.
In UML 2.x, a powertype is a metaclass whose instances are subclasses of a given class. The stereotype has been removed and the powertype is now indicated by typing the generalization set.
In the UML Superstructure 2.4.1 Specification Document[1] the following definition is given:
In UML 2.5.1,[2] the formal definition of powertypes in terms of power sets (or sets of subsets) are no longer given.Instead, powertypes are illustrated through various examples.