Interjection. Not the same at "what's up" which is interrogative.
Whatup is a public request for recognition. It can be used to loudly declare one's success, something akin to "whatnowmothafucka!" (also not a question). Or it can be used as a subdued call for acknowledgement, something like "I told you so".
an intimate gathering of friends and strangers that takes place on a wednesday night and generally involves a fair amount of alcohol in a small dorm room. originally created by 4 south-campus ucla students who needed an alternative to the normal thursday outing.
whatupwednesdays have been evolving, including a theme song, an official shirt that is worn on wednesdays, a constitution, and more. the goal of WW is to be recognized as another day to celebrate during the rough and tough of college life.