A Finite State Machine (FSM) is a computational model used to represent and control the behavior of systems. It consists of a finite number of states, transitions between these states, and actions associated with those transitions. FSMs are widely used in various fields, such as computer science, robotics, game development, and digital circuit design, to model and implement complex systems with predictable behaviors.

Components of FSM:
1. States: Defined conditions or situations of the system (e.g., "Idle", "Processing", "Completed").
2. Transitions: Pathways between states triggered by events or conditions.
3. Inputs/Events: External factors that cause state changes (e.g., button press, time-out, or data reception).
4. Actions/Outputs: Tasks executed during state transitions or while in a specific state.

FSMs can be classified into two types:

Deterministic FSM: Each state has only one possible transition for a given input.
- Non-Deterministic FSM: A state can have multiple possible transitions for the same input.
Applications:
- FSMs are employed in diverse scenarios such as user interface designs, control systems, parsing algorithms, and even artificial intelligence for decision-making in games. For instance, a traffic light controller is a classic example of an FSM with states like "Green", "Yellow", and "Red".

FSMs provide a clear and structured way to design systems with well-defined behaviors, ensuring reliability and predictability.