Many Make-out sluts are out to make out with as many guys as they can in a certain period of time.
Advanced make-out sluts will often keep a list of all the guys she has made-out with and sometimes will even give them grades, whether it be a A-F scale or 1-10 scale.
Rob: Last night was pretty fun, but she's just a make-out slut so I don't think i'll b talking to her anymore. She got what she was trying to get. She's already working on trying to make-out with Drew tonight.
Friend: Did you score?
Jim: No, I've got blue balls. She's such a makeout slut.