short form of "what's up"- simplified as a form of greeting, as in "hi."

what is up.

A Gangster greeting. Another form of the simple "Hi!"

Wassup is another way of saying "What's up". You can also say Wazzup.

Wassup means whats up. Whats up is a way of asking how some one is, and or what someone is doing. Se Wassssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssup.
Most people with an IM start a conversation by saying Wassup, or its shortining sup. Sup can mean the same thing, or a random thing. Only in America

Wuts good..Wuts poppin'... Its thu G'd up way of sayin hi, whats goin on