A transition system is a concept used in theoretical computer science to describe the potential behavior of discrete systems. It consists of states and transitions between these states. The transitions may be labeled with labels chosen from a set, and the same label may appear on more than one transition.
A simple example of a transition system is a finite state machine, which is a device that can be in one of several states (e.g., off, on, idle) and change states according to certain transitions (e.g., turn on when a button is pressed).