Applying UML and Patterns: An Introduction to Object-Oriented Analysis and Design and the Unified Process, Second Edition

25.2. Terminology: Concrete, Abstract, Base, and Addition Use Cases

A concrete use case is initiated by an actor and performs the entire behavior desired by the actor [RUP]. These are the elementary business process use cases. For example, Process Sale is a concrete use case. By contrast, an abstract use case is never instantiated by itself; it is a subfunction use case that is part of another use case. Handle Credit Payment is abstract; it doesn't stand on its own, but is always part of another story, such as Process Sale.

A use case that includes another use case, or that is extended or specialized by another use case is called a base use case. Process Sale is a base use case with respect to the included Handle Credit Payment subfunction use ...