A door is a moving mechanism used to block off, and allow access to, an entrance to or within an enclosed space, such as a building, room or vehicle. Doors normally consist of one or two solid panels, with or without windows, that swing on hinges horizontally. These hinges are attached to the door's edge but there are also doors that slide, fold or spin. The main purpose of a door is to control physical access. Doors are significant in preventing the spread of fire and as a barrier to noise. Many doors are equipped with locking mechanisms to allow entrance to certain people and keep out others. When open, doors admit people, animals, ventilation or light.