Deterministic finite automaton

A deterministic finite automaton (DFA) is like a machine that can do very specific tasks. It is given a set of instructions and then follows those instructions step-by-step. It can look at a word or phrase and determine if it is correct or not based on the instructions it was given. Imagine you have a toy robot that can speak English and you tell it to only say "yes" when you say "hello". That robot is like a DFA. No matter what words you say it will only say "yes" if you say "hello".