The upper half of a bikini is commonly referred to as a bra. The term 'bra' is an abbreviation of the word brassiere, which was first used in the early 1900s. A bra is a form-fitting undergarment designed to support and shape a woman's breasts. It is typically made from a combination of fabrics such as cotton, nylon, and spandex. The bra is an essential part of the bikini, providing support and coverage for the wearer.