As its name suggests, Quicksort is one of the better sort algorithms; it is O(n · log(n)) (though it can be O(n2) in the worst case). In practice it is significantly faster than other algorithms.
Quicksort is a divide-and-conquer algorithm that chooses a pivot value, then partitions the array into two sections with the pivot in its final position roughly in the middle:
|elements ≤ pivot||pivot||elements > pivot|
The outside sections are then sorted recursively.
The partitioning can be done in-place, making Quicksort an in-place sort. Since partitioning is done in-place by swapping elements, Quicksort is not stable.