an expression of greeting. when other guys say "whats up" we try to find the appropriate reply for that. but the fact is that we don't know that what should be the actual response. so this is the term that we are gonna use when we meet with someone or for giving the reply of "whats up".
Aiyar: yo joe wazzup
Waibee: watz down dude
Aiyar: LOL....haven't heard anything like this before
Waibee: Yeaaaaah...itz da latest version...so grab it,try it, fix it and spit it