A door is a movable structure which is used to open and close an entrance, typically consisting of a panel that swings on hinges or that slides or spins inside a space. When open, doors admit people, animals, ventilation, and 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 act as a barrier to noise.