Architecting and designing : UML 2.0 Lite : UML models : UML activity diagram : Decision
  
Decision
A decision is an action with multiple output transitions based on guard conditions.
A decision is represented by the traditional diamond shape, with one or more incoming arrows and with two or more outgoing arrows, each labeled with a distinct guard condition. The guard conditions are input into the definition of the transition.
See also
UML activity diagram