Diapers (nappies) are absorbent products for infants, toddlers, or incontinent adults, featuring a waterproof outer layer, SAP core (holds 400-800ml), nonwoven topsheet, elastic leg/waist gathers, and wetness indicators. Types: disposable tape-style (newborn NB <5kg to size 6 15+kg; Pampers/Huggies brands), pull-ups (toddlers training 9-17kg), swim diapers (non-swelling mesh), cloth reusable (prefolds/pockets/AIO with inserts, eco-friendly). Sizes by weight: NB 2-5kg, S 4-8kg, M 7-12kg, L 9-14kg, XL 12-17kg; hypoallergenic options (fragrance-free, aloe-lined) suit sensitive skin/rash prevention. Change every 2-4hrs; overnight variants extend wear.