Short Definition
Time complexity describes how an algorithm's running time grows as input size grows.
Intuition
It tells you whether the method stays practical as the problem gets bigger.
Technical Definition
Time complexity is usually expressed asymptotically with notation such as O(n), O(n log n), or O(n^2).
Example
A quadratic algorithm may become too slow when input size doubles repeatedly.
Common Misunderstandings
Big-O ignores constants but constants can matter in real systems.
Worst-case complexity is not the only useful performance measure.