In the hotel (hospitality) industry, a room night, or room/night, is a measure of occupancy where a room is the unit of measure.
As opposed to the bed/night occupancy, where one calculates the number of beds in the entire hotel (a room can have more than one) with the nights each of them are booked, like one person (assigned to one bed) for one night.
For example: A hotel has 10 rooms, each with 2 beds. If 5 separate people book 5 rooms for all 30 days in the month of April, this hotel had a room occupancy, or room/night occupancy, of 50% for April. However, there are 20 beds spread out over these 10 rooms. If these same 5 single and separate people booked the 5 rooms for all of April, the bed/night occupancy would be only 25%, because 5 beds were used out of a possible 20 for April.
It can get even more convoluted when you take the nights into consideration. If a hotel with 12 rooms each with 2 beds was booked by 12 separate, single people for 15 each of the 30 days in April, the room occupancy would be 50%, because each room was occupied (100% . . .), but only for 15 of the 30 days (. . . /2 = 50%). However, if you want the bed/night calculation, it would be 25%, because 12 beds were occupied of the 24 available (50% . . .), and for only 15 of the 30 days in April (. . . /2 = 25%). Get it? 🙂