actually, the correct spelling is wassup joe, not what's up joe?. The term means how are you not hi, or hello. It did not come from what's up yo. It came from the last 20 years of urban people using the name joe as a term of endearment; the same way you would use, what's up buddy.
wassup joe, I didn't see you on the block today.
by tiqueda u.l. January 21, 2005