This is a set of two short undergarments. Size 50. Yellow: Purchased at Akachan Honpo, used a few times. White: Received as a gift from the maternity hospital, unused. I didn't use them much because my baby was born in the summer and I often dressed them in combination undergarments. I think these can be used during the newborn period for babies born in winter to spring by putting a coverall over them.