Vestigial organ: An organ that we inherit due to our evolution but no longer has a 'true' function now (mainstream science currently states that there is no completely vestigal organs - basically evolution isn't an exact science so we have vesteges from our past which once served us in a major way that are now mostly (and becoming more) redundant.  So little in fact that we can live happily without them)!

With that in mind the Wisdom teeth are considered vestigial organs (they generally no longer sit in out mouths correctly as our skulls have changed shape so much since wizdom teeth first appeared in our evolutionary past).

You could also kind of say that the coccyx (tail bone) is a vestigial organ, although it helps us sit properly its not needed for this function (or for balance) and we can easily sit correctly without it.  Its basically the end of a tail ..which we once all had when we swung from trees.