A Deterministic Finite Automaton (DFA) is a theoretical model used in computer science to represent and analyze the behavior of systems with a finite number of states. It consists of a set of states, a starting state, a set of accepting states, and a transition function that determines how the system moves from one state to another based on input symbols. DFAs are used in various applications, including lexical analysis in compilers and pattern matching in text processing. They are called "deterministic" because for each state and input symbol, there is exactly one possible next state, ensuring predictable behavior.