Hello. I am currently studying in America to improve my English skill. There is one thing I don't understand. People come to me and say "What's up?" What does that mean and how should I respond to it? Is that sentence same as saying "Hello" ?
'sup?
nothing much
It can be used to mean "hello".
" up
adj.
6. Informal. Taking place; going on: wondered what was up back home. "
http://dictionary.reference.com/search?q=up
" What's going on, what is happening, ... , a colloquialism from the first half of the 1900s, gained currency in the 1940s from Bugs Bunny cartoons in which the rabbit repeatedly says "What's up, Doc?" "
http://dictionary.reference.com/search?q=what's%20cooking
>>1
"What's up?" = "何か（新しいこと）はあったかい？ (what's new?)", "元気かい？ (How are you?)"
そんなに真面目に受け取る必要はないです。単なる普段の挨拶です。特別な話題がないなら、単に "（特に何もないよ）nothing special" とか "（まあまあだよ）so-so" と言えば大丈夫。
You don't have to take it too serious. It's just an everyday greeting. If you don't have a special topic, just saying "nothing special", "Same old stuff" is ok.
ここも参照のこと。
See also:
http://www.amezatsu.com/expression/archives/2004/09/whats_up.html
http://www.amezatsu.com/qa/archives/2005/10/whats_up.html
wazzap
It's also a very casual, informal greeting, used mainly between teenagers or young adults.
It also means "What are you doing?"
文脈によって違うけど、「なにやってんの」って言う意味もあります。
学校でネイティブの先生に What's up? と言われたら、
Not much. って返すのが普通と習ったんだけど、
そういった後どう話を展開させればいいもんなの？
逆にこちらから How about you?って聞き返すのか、
それとも別の話題に入っていいのか。
学校でネイティブの先生に What's up? と言われたら、
Not much. って返すのが普通と習ったんだけど、
そういった後どう話を展開させればいいもんなの？
逆にこちらから How about you?って聞き返すのか、
それとも別の話題に入っていいのか。