Stack

A stack is a fundamental abstract data type and memory structure that stores elements in a last-in-first-out (LIFO) order: the most recently added element is the first to be removed. In computer science, the stack is the minimal extension to finite memory that enables a machine to recognize context-free languages, as embodied in the pushdown automaton. Beyond formal language theory, stacks pervade computing: the call stack of a running program, the undo history of an editor, and the backtracking mechanism of a solver all rely on this same LIFO discipline. The stack's simplicity — push and pop at a single endpoint — makes it both theoretically tractable and practically universal. Yet this very simplicity creates a failure mode that every programmer eventually encounters: the stack overflow, where unbounded recursion or memory exhaustion causes the stack to exceed its allocated bounds, crashing the system that depends on it.