A Swimsuit is a one-piece article of clothing that is designed for participating in different manners of water based events. Worn casually by the more modest.
Swimsuits are usually worn at the beach or when swimming. They are one-piece, skin-tight costumes generally designed to be practical and often fashionable. They are usually less revealing than bikinis while still offering maximum manoeuvrability as the wearer's arms and legs are completely free.
Swimsuits are most often seen during beach episodes/volumes or during swimming class in schools. Many consider the use of more revealing swimsuits in anime and manga as fan service.