A stack overflow error occurs when a program uses more memory on the call stack than is allocated. The call stack is a special area of memory that stores information about active subroutines or functions. When too many functions are called, or when a function calls itself recursively without a proper exit condition, the stack can exceed its limit, leading to this error. This error typically results in the program crashing or terminating unexpectedly. It can happen in various programming languages, including C, Java, and Python. Developers often need to optimize their code or adjust recursion limits to prevent stack overflow errors.