A diaper or a nappy is a type of underwear that allows the wearer to defecate orurinate without the use of a toilet, by absorbing or containing waste products to prevent soiling of outer clothing or the external environment.
When diapers become soiled, they require changing, generally by a second person such as a parent or caregiver. Failure to change a diaper on a sufficiently regular basis can result in skin problems around the area covered by the diaper.