What does 'sup mean?

Answer 1

It means "what's up?"

'Sup is being used as a slang for "what is up" yet another slang for "how are you doing" or "what have you been up to". It's a really informal greeting among close friends.

"Sup" also means to eat supper.

Answer 2

It generally is slang in which a person uses to say "sup" meaning, "what are you doing" or "how is it going" or any others which relate to those mentioned.

Answer 3

It is short for "what's up".

Answer 4

Ate supper.