Architecting and designing : UML 2.0 Lite : UML models : UML Use Case diagram : Use Case Generalization
  
Use Case Generalization
A generalization from Use Case A to Use Case B indicates that A is a specialization of B. Generalization works the same way with Use Cases as it does with classes: the child Use Case inherits the behavior and meaning of the parent Use Case.
See also
UML Use Case diagram