A substance inexplicably present at meetings between close, air-brained math class friends. Also, can be used as a wild card sort of word, when words just don't come to mind but your lips keep moving.
Associated motions: Jazz fingers, followed by a quick jerking "yesssss!" motion with both fists, is commonly understood as sign language for the phrase.
"Man, the purple shit is all over! You know what I'm talking about. It's purple... shit... you totally know."