passenger entrance/exit (of a vehicle)
Refers to the door or opening used by passengers to board or alight from a bus, train, or similar vehicle. Often seen in signs or announcements.
バスの乗降口は前と後ろにあります。
The bus has passenger entrances/exits at the front and rear.
乗降口付近では立ち止まらないでください。
Please do not stand near the passenger entrance/exit.