verb. To have relationships on the side, or to have sexual relations without one's friends having knowlege of the encounters.
noun. The person who acts as the significant other in said events.
Friend 1: I haven't seen Pete around on the weekends lately. What the hell is he up to?
Friend 2: I think he's getting some secret ass.
It wasn't 'till months later that Pete finally got up the courage to introduce his secret ass to his friends.