(idiomatic, informal) A greeting, similar to how are you?; what's happening?; what's up?; what's new?

(colloquial) What is wrong? Why is this happening? / (colloquial, possibly dated) What is happening? What is going on? / (colloquial) How are you?

(idiomatic) furthermore, or in addition, moreover.

Contraction of what is more.

(euphemistic) what the hell

(mildly vulgar, slang) An intensive form of what. / (mildly vulgar, slang) Indicating acceptance, indulgence, or insouciance: Why not? Who cares?

(slang) Used other than figuratively or idiomatically: see that's, what's up. / (slang) Used to express acquiescence or concurrence; true; indeed.

(colloquial, rhetorical question, impolite) A reply to an unimportant or irrelevant statement, indicating indifference on the part of the speaker.

(Ireland) What's happening?

(slang) what is happening?; what's up?