family bath; private bath for families
A private bathing room in a ryokan, onsen, or sento that can be reserved or used by a family group. Often contrasted with larger communal baths.
See also: 旅館
This ryokan has two family baths.
We reserved a family bath and enjoyed the hot spring at our leisure.
貸切風呂 is a private bath that can be reserved by anyone, not necessarily limited to families. 家族風呂 specifically implies a bath intended for family use.
大浴場 is a large communal bath, while 家族風呂 is a smaller, private bath for families.
Compound of 家族 (family) and 風呂 (bath).