Can you explain what a finite state machine (FSM) means in the context of programming and system design?

A Finite State Machine (FSM) is a computational model that describes a system through a finite number of states and transitions between them in response to events or input data. In programming and system design, FSMs are often used to control the behavior of a program, where at each moment the system is in one of the states, and transitions occur according to certain rules.

Example: managing the states of a user interface (for example, a button can be in states "normal", "hovered", "pressed"), or processing protocols where different messages transition the system into different states.

Example in Python:

class TrafficLightFSM:
    def __init__(self):
        self.state = 'RED'

    def on_event(self, event):
        if self.state == 'RED' and event == 'timer':
            self.state = 'GREEN'
        elif self.state == 'GREEN' and event == 'timer':
            self.state = 'YELLOW'
        elif self.state == 'YELLOW' and event == 'timer':
            self.state = 'RED'

traffic_light = TrafficLightFSM()
print(traffic_light.state)  # RED
traffic_light.on_event('timer')
print(traffic_light.state)  # GREEN