When a spouse or other partner only wants sex once a month or less. The sex you get is only out of guilt or obligation, or a mistaken idea this will be enough to keep you from cheating. Usually involves very plain "vanilla" sex with no frills such as wild positions, sex toys, lingerie, etc.
John: "Dude I saw you texting Traci during the game, are you stepping out again?"
Steve: "Man I've been on Welfare Sex for six months."
John: "Oh, cool. Don't get caught."