room rent; rent for a room
Refers specifically to the cost of renting a room, as opposed to an entire apartment or house.
The room rent is 50,000 yen per month.
部屋代を払うのを忘れていた。
I forgot to pay the room rent.
Compound of 部屋 (へや, 'room') and 代 (だい, 'charge' or 'fee').