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Inf. Hello. What is happening? What's up? How're you doing? Hey, Chuck! What's up?
something that you say in order to ask someone what is wrong What's up? Why haven't you left yet? You're quiet - what's up? (often + with ) What's up with Tom? He hasn't spoken all morning.See What's in aid of?, What's the big idea?, What's biting ?, What's the deal?, What's game?, what the hell, What's your poison?, What price [fame etc.]?, What says goes, What's the world coming to?