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 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. Therefore, they are common on ships and in army garrisons, or in places where floorspace needs to be maximized, such as hostels, dormitories, summer camp cabins, or prison cells.
Bunk beds are normally supported by four poles or pillars, one at each corner of the bed. A ladder is used to get to the upper bed, which is normally surrounded by a railing to prevent the sleeper from falling out. Some models also have a privacy curtain for the lower bunk. Because of the need for a ladder and the height of the bed, the top bunk of a bunk bed is not recommended for children under six years of age
A loft bed is an elevated bed similar to a bunk bed, but without the lower beds, freeing floor space for other furniture, such as a desk, which might be built into the loft bed.