Bubble sort is an algorithm that sorts elements.
It works by checking if a case is true and then moving the element up if so until it is not true. It repeats until all elements are in the correct location.
Bubble sort is the most inefficient sorting method because it has to repeat so many times.
Example:

A worst case scenario for bubble sort would be n(n-1)/2
An average scenario would be n(n-1)/4
Best case scenario would be n-1