A pushdown automaton (PDA) is a type of computational model used in computer science to recognize context-free languages. It extends the capabilities of a finite automaton by adding a stack, which allows it to store an unbounded amount of information. This stack enables the PDA to keep track of nested structures, making it suitable for parsing expressions in programming languages and other hierarchical data. PDAs operate by reading input symbols and manipulating the stack based on predefined rules. They can be deterministic or nondeterministic, with the latter allowing multiple possible transitions for a given state and input. This flexibility makes PDAs powerful tools for language recognition and parsing tasks in various applications, including compilers and interpreters.