A Door is a panel or barrier, usually hinged, sliding, or electronic, that is used to cover an opening in a wall or partition going into a building or space. A Door can be opened to give access and closed more or less securely. Doors are nearly universal in buildings of all kinds, allowing passage between the inside and outside, and between internal rooms. When open, they admit ventilation and light. The purpose of a Door closure is primarily to give occupants of a space privacy and security by regulating access to outsiders. For this purpose Doors are equipped with a variety of fittings ranging from simple latches to locks. The Door is also used to control the physical atmosphere within a space by enclosing it, excluding air drafts, so that interiors may be more effectively heated or cooled.

Doors are primarily categorized based on their opening / closure mechanism. A Door may slide along tracks such as High Speed Doors, pivot on hinges fold or may also slide between two wall panels (pocket Door). In the case of rotation, the axis is usually vertical, except in case for garage Doors which opens up horizontally, above the Door opening. Sometimes the axis of rotation is, with a special construction, not in the plane of the Door, on the other side than that in which the Door opens, to reduce the space required on the side to which the Door opens.

Varieties of Doors are offered by Roller Shutter Doors having specific names, depending on their purpose. The most common variety of Door consists of a single rigid panel that fills the Doorway, hinged along one side so that it can fold away from the Doorway in one direction but not in the other. Many variations on this basic design are possible, such as "double" Doors that have two adjacent independent panels hinged on each side of the Doorway. Different types of Doors are available based on the opening mechanism and their utility such as Trapdoor that is oriented horizontally in a floor or ceiling, Stable Door is divided in half horizontally usually to keep pets and domestic animals, Swing Door has special hinges that allow it to open either outwards or inwards, and is usually sprung to keep it closed, Saloon Doors are a pair of lightweight swing Doors often found in public bars, Blind Door is a Door with no visible trim or operable components, Up-and-over Door is often used in garages, Barn Door is a Door on a barn and more. Mostly all type of Doors is made up of strong non restive or corrosive materials for enabling durability and strength. Most commonly Doors are made up of Wood, Steel, Aluminum or Glass.