What is a stack as a data structure?

A stack is a data structure that works on the LIFO (Last In, First Out) principle: last in, first out.

Imagine a stack of plates: to take the bottom one, you need to remove everything on top of it.

A stack has two basic actions:

• push(x): place an element on top of the stack,
• pop(): remove the top element.

Additionally, these are often used:

• peek() / top(): view the top element without removing it,
• isEmpty(): check whether the stack is empty.

A stack is used in:

• handling function calls (call and return),
• undoing actions (undo in editors),
• checking brackets,
• implementing recursion and parsing expressions.