Simple beds are a type of bed that are typically used for sleeping in small spaces. Cots, which are four-letter beds, are usually made of metal or wood and are often used in camping or military settings. Bunks, which are five-letter beds, are two beds stacked on top of each other and are often used in dormitories or shared bedrooms. Futons, which are six-letter beds, are a type of sofa that can be converted into a bed and are often used in apartments or small living spaces.