noun
private bath; reserved bath
Refers to a bath (typically in a shared facility like a ryokan or sento) that is reserved for one person or group's exclusive use during a set time.
旅館で留め風呂を予約した。
I reserved a private bath at the ryokan.
家族でゆっくり入れるように、留め風呂にした。
We chose a reserved bath so the family could relax together.
貸切風呂 also means a bath for exclusive use, but often implies the entire bath facility is rented out, while 留め風呂 emphasizes that the bath is 'stopped' or reserved for a specific person/group during a time slot.
Compound of 留め (tome, 'stopping' or 'reserving') + 風呂 (furo, 'bath'). The term likely originates from the practice of 'stopping' a bath for private use in communal bathing facilities.