A one-piece swimsuit most commonly refers to swimwear worn primarily by women and girls when swimming in the sea or in a swimming pool, playing water polo, or for any activity in the sun, such as sun bathing. Today, the one-piece swimsuit is usually a skin-tight garment that covers the torso, although some designs expose the back or upper chest.

A swimsuit is an item of clothing designed to be worn by people engaging in a water-based activity or water sports, such as swimming, diving and surfing, or sun-orientated activities, such as sun bathing. Different types may be worn by men, women, and children. A swimsuit can be described by various names, some of which are used only in particular locations or for particular types of suit, including swimwear, bathing suit, bathing attire, swimming costume, bathing costume, swimming suit, swimmers, swimming togs, bathers, cossie, or swimming trunks, besides others.