Balconette is a cut or style of brassiere, referred to as the ultimate bra or the best bra ever by many women I have spoken to. The apparent draw of the balconette is the steady support inherent in the bras design, the less constricting straps and the ability to increase cleavage, not unlike a Wonderbra. Contrary to what I would have thought, most girls were more than willing to sell me on the benefits of the balconette, which I found odd seeing as I have little use for one myself. Balconettes are also referred to as demi cup or shelf bras.

As a demi cup style, a contoured underwire supports the breasts, and a large portion of the upper half of the cup found on more traditional bras is removed, exposing the upper part of the breasts. This is a more horizontal cut than is found in most bras. The shoulder straps, which connect lower on the sides of the bra, are set farther apart. This forms a kind of shelf that supports the breast without pressing it back against the chest. The wider set straps can be easily lifted and padding is often added to enhance bust size and cleavage. Balconettes are often referred to as being d'collet‚ and are usually worn when the top of a garment is cut low, wide or square.

As is so often the case, the large breasted girl can have some difficulty with the balconette. The cups of a balconette support only the lower half of the breast, and can be overfilled in a sense. Larger chests can mound up, creating the "dreaded quadruple breast effect", which has the breast spilling over the bra. Not exactly a desired look. There is also the hazard of slipping completely out of the bra. Obviously not the bra to take to the gym.

The term balconette also refers to a Victorian-style iron window treatment, which is essentially a shelf hung on the exterior of windows in a flower box fashion. They normally resemble ironwork fencing, and provide an accent to the window. They are also often used to support creeping vines like ivy.

Thanks to Chiisuta for some extra logistic info