A Nondeterministic Finite Automaton (NFA) is a theoretical model used in computer science to represent and recognize patterns within input strings. Unlike deterministic finite automata, an NFA can have multiple possible transitions for a given state and input symbol, allowing it to explore many paths simultaneously. This flexibility makes NFAs useful for certain types of pattern matching and language recognition. NFAs consist of states, transitions, an initial state, and accepting states. They can process input strings by moving between states based on the defined transitions. If any path through the NFA leads to an accepting state after consuming the entire input, the string is considered accepted by the automaton.