Deterministic Finite Automaton

A Deterministic Finite Automaton (DFA) is a type of Finite Automaton where each state has exactly one transition for each possible input symbol, so there's only ever one path through the machine for a given input string.

See Finite Automaton.

Formally, a DFA is a 5-tuple $(Q, \Sigma, \delta, q_0, F)$: a finite set of states $Q$, an input alphabet $\Sigma$, a transition function $\delta: Q \times \Sigma \to Q$, a start state $q_0$ and a set of accept states $F$. It accepts a string if reading the whole string leaves it in an accept state. The languages DFAs recognise are exactly the Regular Language, the same as a Nondeterministic Finite Automaton.