A combination of a class and a state applicable to that class.
See also activity.
A class with a state machine has many states, each of which characterizes the behavior, values, and constraints of instances that are in the state. In some cases, certain attributes, associations, or operations are valid only when an object is in a certain state or set of states. In other cases, an argument to an operation must be an object in a particular state. Often, these distinctions are simply part of the behavioral models. But sometimes, it is useful to treat the combination of class and state as constraining the value of an object, variable, parameter, or substate. The combination of class and state, treated as a kind of type, is ...