The girl you are sleeping with but she is not your main girl or wife. Normally you go out to a club and you meet a girl and have sex with her. Although the sex was great because you have a main girl or wife you cannot make this chick you main girl so she becomes someone you can have sex with but not a long term relationship. Usually this is a smut who has slept with many other people that ar in your circle of friends.
John: Joan is my shorty on smash because my main girl or wife is pregnant.