The complexity of code in algebraic terms is Big O Notation. In other words Big O Notation determines how efficient your algorithm is!
How is the efficiency of algorithm measured?
In order to measure the efficiency we take into consideration 2 factors.

1. Time Complexity - The time taken to run the code completely

2. Space Complexity - The extra space that is required in the process

It is denoted as -

f(n)=O(inputSize)

Big-O notation show how much time or space an algorithm would require in the worst case scenario as the input size grows.