Definition Non Deterministic Finite Automata

A non-deterministic finite automaton (NDFA/NFA) is a 5-tuple (Q, Σ, δ, q0, F) 

where, 

Q = is a finite set of states. 

Σ = is a finite set of input symbols. 

δ = is a transition function mapping from Q × Σ to 2Q

q0 = is the initial state, q0 ∈ Q. 

F = is a set of final states, F ⊆ Q.

For example,

Consider the NFA that accepts all string ending with 01.

Transition diagram
Transition table

In this NFA, 

M = {Q, Σ, δ, q0, F} 

where, 

Q = {q0, q1, q2}. 

Σ = {0, 1}. 

δ = As shown above. 

q0 = Initial state. 

F = {q2}

Some terms in NFA:

Alphabet: An alphabet is a finite, non-empty set of symbols. 

Generally “Σ” is used to devote the alphabet. 

For example,

Σ = {0, 1} 

Σ = {a, b}

Symbol: Any character, number or special symbol can be treated as a “symbol”. It is the member of the alphabet.

For example,

In above alphabet 0, 1 is symbol.

Word: A word or string is a finite sequence of symbols. 

For example,

S = 0110

S = ababa.