The notation Ο(n) is the formal way of representing the upper bound of an algorithm’s running time.

It calculates the time complexity of the worst-case scenario or the longest period of time an algorithm could take to complete.

**Definition: **

f(n) = O(g(n)) (f is a Big-O of g) or f<= g if there exist constants N and c so that for all n=>N, f(n) <= c.g(n)

Big O really just says that my runtime is sort of bounded above by some multiple of this thing. sometimes you want to say the reverse. sometimes you want to say that I am bounded below. And so there is the different notation for that *Omega Notation* and *Theta Notation* respectively.