In-place sorting algorithm
A sorting algorithm is in-place if the numbers are rearranged within the array A, with at most a constant number of them sorted outside the array at any time.
In-place: Insertion sort, Quicksort, Heapsort
Not in-place: Merge sort, Counting sort, Radix sort
worst-case running time
It is an upper bound on the running time.
The worst case occurs fair often
The average case is often as bad as the worst case