### What
- A **stack** is a linear data structure that **follows the Last In, First Out (LIFO)** principle.
### Complexity Analysis
- Push (Add at top): O(1)
- Pop (Remove from top): O(1)
- Peek (Look at top without removing): O(1)
- Search (based on value/index): O(n)
### Grammar
we use [[Array]] to implement stack in python
```python
stack = []
# Push
stack.append(10)
# Pop
top = stack.pop()
# Peek
top = stack[-1]
# IsEmpty
is_empty = len(stack) == 0
# Size
size = len(stack)
```