A Nondeterministic Pushdown Automaton (NPDA) is a theoretical model used in computer science to recognize context-free languages. It extends the capabilities of a finite automaton by incorporating a stack, which allows it to store an unbounded amount of information. The "nondeterministic" aspect means that the automaton can make multiple choices at each step, enabling it to explore many possible paths simultaneously. NPDAs are particularly useful for parsing nested structures, such as those found in programming languages. They can be represented using formal states, transitions, and a stack alphabet, making them a powerful tool in the study of formal languages and automata theory, closely related to concepts like context-free grammars and compilers.