1. Hooking up with a girl on the side, or using a girl for nothing but sex.
2. A word to describe the girl you keep on the side, just for sex and/or dome; a mistress.
3. A one night stand.
1.) Mike: dude who was that girl in the car with you last night?
Joe: nobody dude, just some bitch I'm using for sideplay.
2.) Raph: Yo dude I saw you and Jackie kiss, is she your girlfriend?
John: Nah, that's just my sideplay chick.
3.) Joe: Dude you like never have a steady girlfriend all I see you do is one night stands...
Steven: Dude, sideplay is perfect. I never have to worry about some bitch being mad at me, I just get pussy.