When a girl straddles her male partner and rubs her pussy on and along the underside of his erect penis, without actual vaginal penetration. May be an adjunct (foreplay, playful coital interlude, serious clit mashing) or alternative to coitus.
Kimmie wants to keep her hymen, but she loves 69ing, anal, and riding the rail.
I love Tina double-edging us by riding the rail, so we supplode together when she finally shoves it in.
by hitting the rail of a pool table. It is used to describe the carom of a pool ball with the rail - usually the "end rail," meaning one of the rails adjascent to the the pocket or other target.