What's “In-place algorithm”?

Here's Wikipedia In-place algorithm excerpt:

In computer science, an in-place algorithm (or in Latin in situ) is an algorithm which transforms input using a data structure with a small, constant amount of extra storage space. The input is usually overwritten by the output as the algorithm executes. An algorithm which is not in-place is sometimes called not-in-place or out-of-place.

for a example of in-place algorithm for reversing a list in {python, perl, emacs lisp, Mathematica}, see: In-place Algorithm for Reversing a List in Perl, Python, Lisp, Mathematica