Architecting and designing : UML 2.5 : Model Elements : Structured Classifiers : Class
  
Class
A class is a classifier which describes a set of objects that share the same features, constraints, and semantics (meaning).
See also
Activity
AssociationClass
FunctionBehavior
Interaction
OpaqueBehavior
State Machine
Stereotype
Device
ExecutionEnvironment
Collaboration
Component
Node
Protocol State Machine
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Structured Classifiers