A bunk bed is a type of bed in which one bed frame is stacked on top of another. The nature of bunk beds allows two people to sleep in the same room while maximizing available floor space. This leads to them being used in places with limited floor space, such as on ships and in army garrisons or in places that wish to maximise bedspace such as: dormitories, summer camp cabins, hostels, children's rooms, prison cells, or university residence halls.
Bunk beds are normally supported by four poles or pillars, one at each corner of the bed. To get to the second bunk a ladder is used, though taller children often find other faster, more creative methods of climbing into them. The top bed is normally surrounded by a railing to prevent the sleeper from falling out, and 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 bunkbed is not recommended for children under six years of age.
The most common type is the standard bunk bed which has two same size mattresses stacked one directly over the other. A twin over full bunk bed is arranged as a standard except that the bottom mattress will be a full size and the upper will be a twin size. A futon bunk is also arranged like a standard bunk except the lower bunk will be a Western-style futon couch which converts into a bed rather than a standard mattress. Futon bunks can be used to save space in small apartments or rooms, because the lower bed converts to a couch for use during the daytime. In an L-shape bunk the bottom bed is oriented at a right angle to the top bed such that when viewed from above the beds form an L. This also creates a small alcove where a desk or bookshelf can be placed.
A loft bed denotes a bunk bed that has only the top bunk, creating an open space underneath that can be occupied by a chest, drawers, or even a work area.  This makes loft beds an efficient use of small spaces by utilizing the entire vertical area that would otherwise be left unused. Some loft beds even have stowable/trundle beds while retaining the capability to contain workstations and drawers. Some loft beds are more expensive than bunk beds due to built-in storage capacity and other features.
A triple lindy loft bed is an arrangement involving a total of three beds. These beds are a combination of bed types, where a loft bed is perpendicularly attached to a bunk bed to form an L-shape.
Bunk beds range in price from economy models made with metal or softwood frames in which the mattresses are supported by metal wire and spring suspension to expensive models made from hardwood which are outfitted with drawers, shelves, and other accessories. Some people make DIY bunk beds from wooden planks and fasteners, either from scratch or using plans or designs that they have purchased.
A bunk bed is a stack of two or more beds. Metal poles or wooden beams connect the bottom bed (called the bottom bunk) to the top bed (called the top bunk). A ladder is used to get up to the top bunk. The ladder is usually attached to the bed.
Bunk beds are often used in children's rooms. Since bunk beds allow a family to put two beds in the space of a single bed, bunk beds save space. Bunk beds help families with small apartments or houses to have enough beds for their children.
Bunk beds are often used in institutions such as prisons. As well, they are often used in public facilities such as homeless shelters and bomb shelters. Bunk beds are also used in firehalls, to give firefighters a place to sleep. Many military organizations use bunk beds. Navy ships and submarines use bunk beds for the sailors to sleep in. Army barracks sometimes have bunk beds for soldiers.
Summer camps and winter cabins for children (such as boy scouts or girl scouts) often have bunk beds. Hostels, a type of inexpensive hotel for travelers, often have bunk beds. Some ski lodges have bunk beds in their rooms.