verb, to have casual sex, to fuck (may be used with preposition on, as "skid on") (usually has derogatory connotation; not the way you'd refer to sex with someone you cared about)
noun, a person inclined to casual sex, a slut (male or female) (someone who is really successful may be called a skidmaster)
Go away, man, I'm skidding in here!
So, did you skid on that Sarah bitch the other night?
That Kassie is such a wild skid!