What is stack?

A stack is a data structure that works on the principle of Last-In-First-Out (LIFO). This means that the last item pushed or added to the stack is the first item to be taken out or removed from the stack.

A stack has two primary operations: push and pop. When an item is pushed, it is added to the top of the stack. Similarly, when an item is popped, the top item is removed from the stack.

A stack can be implemented using arrays or linked lists. In an array-based implementation, the elements are stored in contiguous memory locations. In a linked list-based implementation, the elements are stored in nodes that contain a reference to the next element in the stack.

Stacks are widely used in computer programming, particularly in the implementation of recursive algorithms, parsing expressions, and managing function calls. They are also used in operating systems to manage memory allocation and in web browsers to implement the back and forward buttons.