What is a quick sort?

Perhaps not unsurprisingly given the name of the algorithm, the quicksort orders a data set extremely quickly using divide and conquer.  The principle of divide and conquer is to create two or more identical, smaller sub-problems from the larger problem, before solving them individually and combining their solutions to solve the bigger problem. 

The algorithm makes use a of a pivot value from the data set, against which other items are compared to determine their position.  It is often considered more efficient than a merge sort due to requiring less memory than a typical recursive merge sort implementation, but this is not really the case.  It is usually dependent on the factors

affecting the algorithm such as the data set being sorted and the pivot chosen.