This term is used to describe the act of performing cunnilingus and/or intercourse after the female has come home from the gym and before she showers. The sweaty female vagina enhances the flavor and the release of endorphins after exercise by the woman increases the joy of sweaty sex. Though it should be noted that a vagina must be clean first prior to getting sweaty from a heavy workout.
"I was so horny we did it post gym pre shower. It was delicious."
Guy: You look so hot I want you now!
Girl: I'm all sweaty from the gym
Guy: Post gym pre shower baby.