A bikini or two-piece is a type of women's swimsuit, characterized by two separate parts — one covering the breasts, the other the groin (and optionally the buttocks), leaving an uncovered area between the two garments. It is often worn in hot weather and while swimming. The shapes of both parts of a bikini closely resemble women's underwear, and the lower part of a bikini can therefore range from the more revealing thong or g-string to briefs and the more modest square-cut shorts.

Two-piece garments worn by women for athletic purposes have been observed on Greek urns and paintings, dated as early as 1400 BC. Ancient artwork from over 1700 years ago in Villa Romana del Casale have depicted women in garments resembling modern-day bikinis. [1]

Sometimes the term bikini is used to describe the type of man's swimsuit also known as a speedo although real men's bikini swimsuits do exist that are not brief like.