A deterministic finite automaton (DFA) is a theoretical model used in computer science to represent and recognize patterns within input strings. It consists of a finite number of states, including one start state and one or more accept states. The DFA processes input symbols one at a time, transitioning between states based on a defined set of rules, ensuring that for each state and input symbol, there is exactly one possible next state. DFAs are used in various applications, such as lexical analysis in compilers and pattern matching in text processing. They are efficient because they require only a single pass through the input, making them faster than other types of automata, like nondeterministic finite automata (NFA).