The term “strap-on” is often used to refer to the entire assembly of a harness and dildo, including a strapless strap-on. The strap-on harness is something you wear on your body, such as a thong or jockstrap, or even an underwear harness. Dildos are typically inserted into the harness’s O-ring, but strap-on harnesses may be equipped with a dildo already built into them.