noun which may take the genitive case particle 'no'
for adults; for use by adults
Used to describe items, facilities, or content intended for adults, often in contrast to children's versions.
This pool has lanes for adults.
大人用のおむつも販売しています。
We also sell adult diapers.
子供用 describes something made for children, while 大人用 describes the same kind of thing made for adults.
Compound of 大人 (otona, 'adult') + 用 (yō, 'for use').