NFA - Non-deterministic Finite Automaton, aka NFSM (Non-deterministic Finite State Machine)

The state machine described in the previous section is a deterministic finite automaton, in which each state is unique. What would make a finite automaton nondeterministic is if each state was not. For the example, if the state machine allowed the input to have any letter as the second letter for the word "person" to transition to the next, then the next state would not be unique, making it a nondeterministic finite automaton.

Deterministic finite state automata

In general, finite state machines can model regular grammars.

Deterministic finite automata can represent deterministic context-free grammars.

Non-deterministic finite automata can represent context-free grammars.

A deterministic Finite Automata)DFA will have a single possible output for a given input.The answer is deterministic because you can always feel what the output will be.

A (Nondeterministic Finite Automata)NFA will have at least one input which will cause a "choice" to be made during a state transition,unlike a (deterministic Finite Automata)DFA one input can cause multiple outputs for a given (Nondeterministic Finite Automata)NFA.