Based on the original Barter System. Used when someone gets injured and they are worried a cast, crutches, stitches ETC will negatively impact their sex life. This is an economically friendly way to get serviced with out resorting to prostitution.
She was writing the definition of the Barner System and it gave me a boner. Maybe I'll use my boner to service her in return, and consequentially, utilize the Barner System.