Bunk bed

A bunk bed is a type of bed in which one bed frame is stacked on top of another. No box spring is required as the mattress lies on a flat surface, the bunkie (or bunky) board, and may be surrounded by rails. The nature of bunk beds allows two or more people to sleep in the same room while maximizing available floor space for activities. This leads to them being used in places with limited floor space, such as on ships and in army garrisons or in places where floorspace needs to be maximized, such as dormitories, summer camp cabins, hostels, children's rooms, prison cells, or university residence halls.