A wing is the portion of the side and back panels of a bra that go around the body. The wing forms the main section of the bra along with the bra's cups.
The wing sections of a bra are actually very important in regards to the bra's design. Each one has its own purpose. The side wing is mean to give the bra wearer more support and a more slimming appearance. Depending on what the bra is made of, a side wing helps to hold in the flabby fat that some women have and keep it from hanging over the edges of the bra.
Most bras' side wing is made of a stretchy nylon-spandex mix to allow for give and take of the body's movement, however, it can be made of cotton, lace, silk or other material. There is even a type of side wing that is made of an adhesive material so women don't have to do anything except stick the bra to their chest. This is so that there is no need for straps that would otherwise show in a strapless dress.
A back wing is another section of the makeup of a bra's design. A back wing is the piece of material that goes from the bottom of the bra cup in the front down to the back of the bra. A back wing helps to hold the bra in place, thus giving the woman more even and dedicated support for her breasts.
One important note is to be aware of the different types and styles of both a back wing and a side wing style of bra. It is important to know if the fabric of a side wing or back wing stretches and how much it stretches, so you will know how well it will fit with the style of clothing you want to wear it with.
The back wing is where the hooks and fasteners of bras are located, so this area needs to be made of strong material and be properly secured to the fabric so it won't come loose.
Overall, both a back wing and a side wing give more coverage and more support for a woman's body when she wears a corresponding bra. These designs shape and smooth the area of the sides and back and are sometimes reinforced for extra strength, as well as have additional smoothing panels to help get rid of unsightly bulges so your clothes look smooth and neat.