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.