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 the following definition is given:
The notion of power type was inspired by the notion of power set. A power set is defined as a set whose instances are subsets. In essence, then, a power type is a class whose instances are subclasses.
References:
References
Powertype (UML) Wikipedia(Text) CC BY-SA