Shop Urban Outfitters' assortment of one piece bathing suits. Our collection comes in a variety of styles and colors to help you stand out on the beach. Sign up. A one-piece swimsuit most commonly refers to swimwear worn by women and girls when swimming in the sea or in a swimming pool, or for any activity in the sun, such as sun bathing. Today, the one-piece swimsuit is usually a skin-tight garment that covers a.