When you notice you have a cut somewhere but have no recollection of where it is from.
Steve: "I swear I had 5 fingers last time i looked. Meh nvm."
Gary: "Holy shit dude, you got yourself a pretty serious ghost cut!"
When a person leaves without saying a word and then later claims that they had something important to do when in reality they had nothing to do but just wanted to leave without saying goodbye.
Friend 1: Did anyone see where Danny went?
Friend 2: I just got a text from him saying, "Gotta go man, you know got shit to do, UHH."
Friend 3: Damn, he just ghost cut.