A bikini is a women’s two-piece swimsuit featuring two triangles of fabric on top that cover the woman’s breasts, and two triangles of fabric on the bottom: the front covering the pelvis but exposing the navel, and the back covering the buttocks. The size of the top and bottom can vary, from bikinis that offer full coverage of the breasts, pelvis, and buttocks, to more revealing designs with a thong or G-string bottom that covers only the mons pubis, but exposes the buttocks, and a top that covers little more than the areolae.
While the name “bikini” was at first applied only to beachwear that revealed the wearer’s navel, today the fashion industry considers any two-piece swimsuit a bikini. Modern bikini fashions are characterized by a simple, brief design: two triangles of fabric that form a bra and cover the woman’s breasts and a third that forms a panty cut below the navel that covers the groin and the buttocks.
Bikinis can and have been made out of almost every possible clothing material, and the fabrics and other materials used to make bikinis are an essential element of their design. Modern bikinis were first made of cotton and jersey, but in the 1960s, Lycra became the common material. Alternative swimwear fabrics such as velvet, leather, and crocheted squares surfaced in the early 1970s.