“What’s up?” is a greeting whose meaning is mostly irrelevant in that the asker doesn’t want an answer to the literal question which means something like “What is new?”
or “What’s happening (right now/in your life)?”.
The simplest response if you don’t have information you want to share immediately with the asker is probably just to say something like “not much”, “not too much”, or “hey (man/dude)”.
If you’re offered “what’s up” in response to a greeting of your own, you should read it as a request for you to proceed to the content part of what you want to talk about.
english.stackexchange.com/users/39/nohat
"Not much, how about you?"
Unless, of course, you are in the midst of something exceptional.
It's just a greeting meaning "What is happening?", and a reply that nothing's happening means you're fine.
english.stackexchange.com/users/16829/Paul Richter
Depends on the tone in which it's asked - with the right tone, it can be synonymous with "What's wrong?
", where, with a less concerned tone, it's more of a "How are you?".
I'd reply very similarly to either.
english.stackexchange.com/users/1010/Rowland Shaw
That is an expression that has about as much meaningfulness as "How are you?"
or "How's it going?"
All, including "What's up?" are used as greetings.
Now, each can be taken literally where someone may want to truly know "how you are", particularly if you've been sick, for instance, but all those terms are very commonly used along with the traditional greeting words, "Hi, "Hello", "Hey".
Responses?
What's up?
-
"Not much, how about with you?"
How are you?
- "Fine, and you?"
How's it going?
- "OK.
How's it going with you?"
english.stackexchange.com/users/25824/Kristina Lopez
If you want to be unconventional, you can reply "the sun" or "me, barely."
That usually gives people pause.
english.stackexchange.com/users/67/moioci
It used to be asked only when the person addressed seemed to be in some kind of trouble.
Some people, I believe, now use it as a simple greeting.
I've never been greeted in this way myself, so I can only speculate that the reply might be something like '
Yeh, I'm good.'
english.stackexchange.com/users/12952/Barrie England
Options: Not much, what's up with you?
Oh, the usual.
Hey!
english.stackexchange.com/users/31020/histocrat
To directly reply to "What's up?"
(as a rhetorical question), "'sup" does the job.
(American)
english.stackexchange.com/users/549/mfg
"Stuff, y'know." (The same stuff keeps happening like it happens all the time.
You already know what kind of stuff.)
english.stackexchange.com/users/14666/Kris
You can respond using this (pick one): Thank God, I am doing well (or:
Unfortunately, I'm not doing so well today, or: Everything is in order, or: Not much, et al.).
I think it is acceptable as well to reply back with the same greeting: How are you doing (today/tonight/this morning/
this afternoon/this evening)?
english.stackexchange.com/users/21239/Adam Mosheh
Sorry if it's a trivial question, but when someone uses  what's up  as a greeting I have no idea what they want to hear. What are the possible answers and what does this question mean exactly?
What is an appropriate response to "what's up" greeting?
english.stackexchange.com
<slang><greetings>
english.stackexchange.com/questions/2471
english.stackexchange.com/users/13/serg
The simplest response to a "what's up?" greeting is simply "not too much" or "hey". If someone says "what's up" in response to your own greeting, this would be a request for you to proceed to what you want to talk about. Some people may simply respond "yeah, I'm good." This is a greeting and the simplest response is probably just to say something like “not much”, “not too much”, or “hey”.
The simplest response to a "what's up?" greeting is simply "not too much" or "hey". If someone says "what's up" in response to your own greeting, this would be a request for you to proceed to what you want to talk about. Some people may simply respond "yeah, I'm good."  “What’s up?” is a greeting whose meaning is mostly irrelevant in that the asker doesn’t want an answer to the literal question which means something like “What is new?” That is an expression that has about as much meaningfulness as "How are you?" I think it is acceptable as well to reply back with the same greeting:   How are you doing (today/tonight/this morning/. The simplest response if you don’t have information you want to share immediately with the asker is probably just to say something like “not much”, “not too much”, or “hey (man/dude)”.
 “What’s up?” is a greeting whose meaning is mostly irrelevant in that the asker doesn’t necessarily want an answer. If you’re offered “what’s up” in response to a greeting of your own, you should read it as a request for you to proceed to the content part of what you want to talk about. "What's up?" is simply a greeting and shouldn't be taken literally. You can simply respond, "Not much, how about you?", although you might want to answer the question literally for comic effect. If, however, you receive this question as a response to your own greeting, you should take that as an indicator to keep talking.
The simplest response is probably just to say something like “not much”, “not too much”, or “hey”.  In the past it would be asked only when the person addressed seemed to be in some kind of trouble - now it's a simple greetings.
 “What’s up?” is a greeting whose meaning is mostly irrelevant in that the asker doesn’t want an answer to the literal question which means something like “What is new?” That is an expression that has about as much meaningfulness as "How are you?" I think it is acceptable as well to reply back with the same greeting:   How are you doing (today/tonight/this morning/. The simplest response if you don’t have information you want to share immediately with the asker is probably just to say something like “not much”, “not too much”, or “hey (man/dude)”.
This is simply a greeting and should not be taken literally. The most common response would be to say simply, "Not much, how about you?", although you can always answer literally if you want to be humorous. If some says "What's up?" after your initial greeting, you should take it as an indicator to continue talking.