Also known as specialise
Refinement of a state refers to the process of converting an atomic state to a compound state by introducing substates. This is done to change the behaviour of the state in question, typically by virtue of the substates handling (and therefore consuming) some, or all events before the refined state.
For example, a state A could react to the event ε1 by transitioning to the state B, and react to the event ε2 by transitioning to state C . If it is desirable that the ε2 transition to state C should only be valid after, say, one second, the atomic state A can be converted to a compound state A by introducing a couple of substates. The ε2 event from A to C could then be moved to one of those substates.
The act of introducing these substates to change A’s behaviour, is called a refining, or specialising state A.
Both substates can be called be refinements, or specialisations of state A.