Purity is a song that appeared on the first Roadrunner Records release, self-titled album "Slipknot" alongside the song Frail Limb Nursery. This song was the cause of the album's rerelease due to the possible uprising of a lawsuit.
The song is about a girl named Purity Knight that was apparently brutally kidnapped and buried alive, the story was fabricated by crimescene and is ultimately untrue. Corey however found the story at Crimescene.com and, not knowing it was untrue, wrote a song about it; transforming the demo "Despise" into the song "Purity". As a result it was placed onto Slipknot's first Roadrunner outing.
On a lighter note the owner of crimescene.com has been grateful to Slipknot for a significant increase in hits and thus we may be able to hear Purity once again... (maybe as a rerelease). The song has recenty been confirmed for a rerelease on the band's upcoming DVD release.
The album was originally released with Frail Limb Nursery and Purity as tracks 8 and 9, but Slipknot had to re-release the album without those tracks. In their place, Slipknot decided to put 'Me Inside', which I believe was supposed to be a digi-pak song.
Purity and Frail Limb Nursery were removed because of a legal dispute. I believe Corey read the Purity story on the internet and thought it was real and wrote a song about it, but it wasn't real, so it was copyrighted. When crimescene.com found out about this they threatened to sue Slipknot.