Commonly used in the black community but also used in white suburbia as a way of saying "Hello, how are you/ What is going on". The saying originated in the fine city of Detroit, Michigan.
During a phone call.....
Dope Fiend: Hello
Dealer: What up doe Dope Fiend: You got tha hard??
Dealer: Nigga stop playin on my mutha fuckin phone, you know i got what you need.
Dope Fiend: Bet, let me get a fat dub.
Dealer: Nigga meet me at the liquor store on Westwood.
Dope Fiend: Aight bet it up, 100