look up any word, like sex:
 
1.
An extremely annoying question that has (unfortunately) replaced "Hello" or "Hi" as the most popular form of casual greeting. For full effect, best delivered while walking past someone at about 90 m.p.h. so the person you're talking to has no time to respond, and in a tone that suggests you really don't give a shit about "what's up" with them.
Dude #1: "Hey, man. What's up?"
Dude #2: "Uh..." (what he managed to get out before Dude #1 was already too far away to hear the rest of what he was going to say)
by der ubergeek February 09, 2005
 
2.
see also: whazzup, whassup, whasabi!!, etc.
1. Hi
2. Wtf is wrong with you??

It's probably originated from the late 20th century, when people were astounded with the sky. The only thing that they would reply was "nothing"

Probably the first term to the decline of western civilization
1. Person 1: What's up?
Person 2: "Nothing" (most common response, maybe 99% of people say that)

2. Person 1: What's up?
Person: "The sky" (smart alleck answer: also: "the ceiling" or, "da roof")
 
3.
Possibly derived from "what's the update." Extremely overused, almost exclusively by America's youth.
Sometimes I wonder why people always ask each other the same question over and over again, when answer is always "nothing." Are we really that dull?
Mike: What's up?
Matthew: Nothing. If you ask me again I'll roast you.
by Renaissance Woman 4 u January 08, 2005
 
4.
what's happening with you?

also lookup:
word up
sup
wizzup
hey, whats up?
by actionsketch November 26, 2003
 
5.
1. A casual greeting or conversation starter, somewhat of a rhetorical question.
Usually followed by something like "Not much, you?," "Nothing much," or even answered with a "Hey man, how's it going?"
syn: How's it going? What is new?

2. syn. What can i do for you?, What would you like? What's on your mind?
1. Person #1: Hey There! What's up?
Person #2: Oh not much. What's up with you?

2. Person #1: Hey come here for a second, I have to ask you something.
Person #2: Ok, what's up?
by GangstaRL December 19, 2005
 
6.
What is happening wiht you, How are you, whats going on?
Something that LouAnn doesnt understand.

Usual response: Nothin Much
**Do not reply 'HI' or with another 'Whats Up'**

A common phrase that most people understand & use each day.
Carl: Hey Dude
Mark: Hey Whats up?
Carl: nothin much
Mark: Cool
by Ednabrowneye13 January 17, 2009
 
7.
How people who are too lazy to add a single apostrophe to a word, spell the phrase, "What's up?" (What-is-up?).
Man: Hey man! Whats up! I'm so lazy that I decided to leave the apostrophe out of "what's", that way I can conserve more energy. You know, because I oppose global warming and all that.
by Hold My Umbrella June 14, 2011