whats up?

could someone tell me the meaning of “whats up”?
someone told me it means “whats new, whats going on” etc…
a friend from USA told me that it means “what are you doing”…
I am confused…please help me.

It can mean all those things.

Note the apostrophe:
what’s

***** NOT A TEACHER *****

Hello, Coolrus:

I am an old man, so I am not cool like you (“COOLrus”).

But here in the United States, some cool people do not ask “What’s up?” They simply look at you and ask:

'sup? (What’s up?)

James

thank you so much for your kind reply…but could you please tell me in what context it can mean all these?
suppose i am going to talk to a friend on phone, i just ask him “what’s up” as a starter.
In this context, what does it mean?

***** NOT A TEACHER *****

Tom (your friend hears the telephone ring. He picks it up): Hello.
Coolrus: 'Sup, dude?
Tom: Not much! Just hanging out [relaxing], dude. And you?
Coolrus: Yeah, I’m just hanging, too.
Tom: So what are your plans for today?
Coolrus: Nothing. Want to hang (out) together?
Tom: I’m down with that [I agree to that].
Coolrus: Let’s meet at McDonald’s at noon!
Tom: OK, dude. Later! [I’ll see you later]


Just a gentle reminder: it is necessary to ALWAYS capitalize the personal pronoun “I.”

James

I don’t know how to thank you , Mr. James. You made it so clear to me.
I am all clear now. Thanks again.

My pleasure.

Just to confuse matters then…

The context above is correct, but if you were to make one change to the context, then ‘what’s up’ would have a different meaning:

Tom: Hi! I got your message but this is the first chance I’ve had to call you back. What’s up?
What’s up? = what’s the matter? / What do you want?

Very important distinction, Beeesneees. Very important for Coolrus to know, indeed.

Tom (calls Coolrus): Are you sitting down?
Coolrus: Yes, I am. What’s up? ( = What’s the problem?) (This time, “What’s up” is not a general greeting, so I do not think that it would be appropriate to say " ‘sup?’ ")
Tom: Now don’t get excited, but I hear that Mona, your girlfriend, is secretly seeing another guy besides you!
Coolrus: No problem.
Tom: Why not?
Coolrus: Because I am secretly seeing another girl besides Mona!
Tom: Cool!

Thank you so much, Mr. James and Mrs. Beeesneees.
I used to use “what’s up” to mean “what’s the matter” as in the context provided by Mrs. Beeesneees. I was quite familiar with this context. I often ask my friend “what’s up” when he/she looks like something has happened to him/her or something’s wrong with him /her. i had no idea of how to use “what’s up” as greeting. It did sound like something unfamiliar or meaningless when someone greeted me as “what’s up”. Now that you have explained it to me clearly, i can understand its uses.
Thanks again.