A door is a moving structure used to block off, and allow access to, an entrance to or within an enclosed space, such as a building or vehicle. Similar exterior structures are called gates. Typically, doors have an interior side that faces the inside of a space and an exterior side that faces the outside of that space. While in some cases the interior side of a door may match its exterior side, in other cases there are sharp contrasts between the two sides, such as in the case of the vehicle door. Doors normally consist of a panel that swings on hinges or that slides or spins inside of a space.

When open, doors admit people, animals, ventilation or light. The door is used to control the physical atmosphere within a space by enclosing the air drafts, so that interiors may be more effectively heated or cooled. Doors are significant in preventing the spread of fire. They also act as a barrier to noise. Many doors are equipped with locking mechanisms to allow entrance to certain people and keep out others. As a form of courtesy and civility, people often knock before opening a door and entering a room.

Simon Godfried Albert Doorenbos (7 October 1891, Barneveld – 1980) was a Dutch horticulturist best known for his work as Director of The Hague Parks Department from 1927 until his retirement in 1957, with a brief interruption during the Second World War when he was dismissed and evicted by the Nazis for refusing to remove trees and shrubs to facilitate the construction of a V1 flying bomb launch pad.

Doorenbos started his career as a nursery representative in 1915, visiting the UK and USA. His long career was distinguished by the raising of a number of important cultivars, including Symphoricarpos × doorenbosii, Betula utilis 'Doorenbos', and numerous Dahlias. Perhaps his most famous achievement was the hybrid elm cultivar 'Den Haag', indeed it has been postulated that he was the first to think of crossing elms to obtain varieties resistant to Dutch elm disease. Doorenbos was also responsible for the introduction of the Himalayan Elm Ulmus wallichiana to Europe, cuttings of which he obtained from the Arnold Arboretum in 1929; the species was later to play a major role in the Dutch elm breeding programme.

A door is a panel or barrier used to cover an opening in a wall or partition.

Door or doors may also refer to:

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