A non-smoking room (often used interchangeably with 禁煙室), a room where smoking is prohibited.
今回は禁煙ルームを選んだので、タバコのにおいがしなかった。
I chose a non-smoking room this time, so there was no smell of cigarettes.
駅前のビジネスホテルは禁煙ルームが多い。
Business hotels near the station often have many non-smoking rooms.
チェックインのときに禁煙ルームを希望すると伝えた。
I told them at check-in that I preferred a non-smoking room.