Architecting and designing : UML 2.5 : Model Elements : Structured Classifiers : Interaction
  
Interaction
UML specifies several types of behaviors:
Activity
State Machine
Interaction
Opaque Behavior, which has subtype FunctionBehavior
Interaction is a communication between objects. You model Interactions on Sequence diagrams.
See also
Class
Activity
AssociationClass
FunctionBehavior
OpaqueBehavior
State Machine
Stereotype
Device
ExecutionEnvironment
Collaboration
Component
Node
Protocol State Machine
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Structured Classifiers