The strapless bras unlike the backless bra are bra that don't have the straps that go over your shoulders. As the backless models don't have a band that goes behind your back and might include models that have some sort of straps. Even though the normal "two-cups" model is what I would call a backless strapless bra. It is very useful in situations where one is wearing a top that does not have sleeves or the so called tube-tops that stop just over ones breasts. This way you don't have the annoying straps showing and everyone does not have to see what color bras you are wearing.