Event

An event is a significant or noteworthy occurrence

For example a phone is taken of the hook

The event which trigger a state change can be added to the transition lines on a state diagram. The action which actually moves the object into the new state can also be specified. There are referred to as trigger events and actions. If an event occurs without an explicit trigger, such as would occur if a state completes an activity then moves to the next state, it is referred to as a trigger-less transition