Wiktionary
what up
interj. (context slang English) (alternative form of what's up English)
Wikipedia
What Up
"'What Up?'" is a posthumous single by American rapper Pimp C, featuring rapper Drake and former-fellow UGK member Bun B. It's the lead single from Pimp C's first posthumous studio album, and third studio album over all, The Naked Soul of Sweet Jones.