What is a Racerback Bra?  

A bra with V-shaped or x-shaped straps in the back which meet between the shoulder blades is a racerback bra. It's back design prevents straps from slipping off your shoulders and is an  excellent solution for sleeveless tops where traditional bra straps might be visible. This design can take many shapes. Some may take the form of a panel that covers the center of your back, and others can be as simple as straps that connect at the center of the back of the bra. J-hooks are an easy way to achieve this same effect by bringing the straps closer  together on the back, while also keeping the option of the traditional strap configuration.