Auto Tuning (according to wikipedia) 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, and has allowed singers to perform perfectly tuned vocal tracks without the need of singing in tune."

For a fun example of the above, check out this great video of an auto tuned dog.