A greeting used to bid tiding to an attractive girl. Can also be used as a greeting to a man, either stranger or friend. Note that using this greeting at a man does not indicate homosexuality, but rather an example of how cool you truly are by showing that you do not give a fuck.
As said to a girl you pass on the street: "Sup girl!?"
Can also be used with a qualifing descriptor to highlight one particular girl out of a group: "Sup girl...........on the left"