What it sounds like, and the records to hear it on.
Auto-Tune is a proprietary audio processor created by Antares Audio Technologies. Auto-Tune uses a phase vocoder to correct pitch in vocal and instrumental performances. It is used to disguise off-key inaccuracies and mistakes to allow for less takes in a studio. While its main purpose is to slightly bend sung pitches to the nearest true semitone (to the exact pitch of the nearest tone in traditional equal temperament), Auto-Tune can be used as an effect to distort the human voice when pitch is raised/lowered significantly. .