The act of preemptively cheating on your significant other *just in case* they cheat/are cheating on you. That way if they ever cheat, you have an ace in the hole.
Very similar to the well documented Prisoner's Dilemma.
Guy 1: You hooked up with Emily? Thought you had a girlfriend
Guy 2: It was just insurance, nothing serious
Guy 1: You don't trust your girl?
Guy 2: She went on Spring Break with a bunch of dudes, WTF am I supposed to think?
Guy 1: Yeah I feel you