O(1) Constant Time:
An algorithm is said to run in constant time if it requires the same amount of time regardless of the input size.

O(n) Linear Time:
An algorithm is said to run in linear time if its time execution is directly proportional to the input size, i.e. time grows linearly as input size increases.

O(log(n)) Logarithmic Time:
An algorithm is said to run in logarithmic time if its time execution is proportional to the logarithm of the input size.

O(n^{2}) Quadratic Time:
An algorithm is said to run in quadratic time if its time execution is proportional to the square of the input size.