A baby bodysuit is a type of clothing designed for infants and toddlers. It is usually made of cotton or a cotton blend and covers the torso and legs. It is often referred to as an 'onesie, ' which is a term derived from the brand name of a popular baby bodysuit. Onesies are typically worn as an undershirt or as a sleepwear garment. They are also used as a base layer for other clothing items such as sweaters and jackets.