The back is one of the important erogenous zones on the body and the exposure of the back is detailed at backage, which also includes a discussion of the various body landmarks.
This section discusses various back styles and their relationship to fashion lines. The names of these styles all derive from letterland, where the shape of the letter approximates the silhouette of the fashion lines: the T-back, X-back, U-back, and V-back. These developments accelerate after the early 1980s.
The T-back, also called a racer back, is a silhouette with four fashion lines--two armholes, a neckline, and a cutoff. Its letter is formed by the shape of the fabric: the narrow body of the T forms a vertical swath up the spine, and the top horizontal bar of the T marks a narrow collar which passés around the left and right of the neck and then widens in the front to pass across the top of the breasts, under the armpits, and descends around to the center back again (WB8603). In this sense the T-back may be thought of as a bra with very large armholes; it leaves the shoulder blades bare, and is most typically bare-midriffed, although waistline and purpose can vary (VB8603). When made of thick Spandex it is a favorite for athletic support: there are no straps to fall off and the breasts are firmly contained (NYA27S, NYA3F6).
Note that T-back also appears in maillot (DR8510, CI9008). The T-back maillot, like the V, gathers vertical tension from the center of the back, but unlike the V, does not split the straps, rising instead up the spine to the back of the neck, where it collars around to the front.
The T-back maillot tanga reinforces the silhouette in a daring way (V8701, EL8801).
Like the X, T frames and glamorizes the shoulder blades. In bikini, T regresses undershirt and opens armhole tanks, but in maillot it allows the armhole to sweep around the top of the hips and up center-front, possibly toplessing the wearer.
One variation on the T-back is the T-front, in which the neckline descends between the breasts to a point below before widening out into a waistline. The T-front, especially the T-front maillot, may be worn solo (and topless) or with an accompanying top, a bandeau being typical.
The T-back soutien-gorge is also comboed on the beach with another T-back, the T-back culotte, which also gets its name from its letter shape, and which even the neophyte bikini scientist will recognize as an alias for a tanga (PB87BC).
The X-back almost always involves a criss-cross of some kind of another. It appears in the maillot species prior to 1930s (CB2L20) and again in the 1980s in an x-backed maillot g-string (CB8101, BC8301). This may involve a crossing of the bra straps as with a string top, either casually, or in a suit designed to be tied in this manner (CB7501, Vero8408).
X-backs are also constructed into sportswear designed to be worn on the street or on the way to and from the beach, usually without any supporting undergarment.