A person you see at bars or parties that you always greet by either head-nod, handshake, or ever-popular "what up." However, the name of this person, along with all other personal information is unknown.
Guy: "Whats-up buddy"?
Whats-up buddy: "Hey bro"
(they walk right by eachother, no further communication)
Guy to his girlfriend: "Shit, I see that guy around all the time, but I don't have a clue what his name is"