Stack is a linear data structure which follows a particular order in which the operations are performed. They may be LIFO(Last In First Out ) or FILO(First IN Last Out).


Mainly the following three basic operations are performed in the stack:
1. Push
2. Pop
3. Peek

1. Push: Adds an item in the stack. If the stack is full, then it is said to be an Overflow condition.

2. Pop: Removes an item from the stack. If the stack is empty, then it is said to be an Underflow condition. The items are popped in the reversed order in which they are pushed.

3. Peek: Get the topmost item. In many books it is referred to as top.


How to understand a stack practically?
There are many real life examples of stack. Consider the simple example of Books stacked over one another  in Library. The book which is at the top is the first one to be removed, i.e. the book which has been placed at the bottommost position remains in the stack for the longest period of time. So, it can be simply seen to follow LIFO/FILO order.