What does 'What's up' mean?

Answer 1

It is an informal greeting meaning "How's it going?" or "What's new?"

it means "hey" or "whats up?" "hows it goin?"

how's it going. hey. how you doing. what goes on
It literally means something like," What is going on in your life? " ," What have you been doing recently? ". Often it is just another way of saying "Hello "or "How is it is going?" It does not really mean anything but is just a way of making a greeting.