尿不湿 literally 'pee doesn't wet'. It started as a brand name (1990s) that became the generic word for disposable diapers, the way 'Kleenex' did for tissues. More formal: 纸尿裤.
usage
Dominant brands in China: 花王 (Kao Merries, Japan), 帮宝适 (Pampers), 好奇 (Huggies), and domestic 巴布豆.
