A door is a panel that covers an opening in a building, room or vehicle. Doors are usually made of a hard, semi-permeable, and hard-to-break substance (such as wood or metal), but sometimes consisting of a hard frame into which windows or screens have been fitted. Doors are often attached by hinges to a frame. Doors make ingress into or egress from a building, room, or vehicle easier to manage. The panel may be moved in various ways (at angles away from the frame, by sliding on a plane parallel to the frame, by folding in angles on a parallel plane, or by spinning along an axis at the center of the frame) to allow or prevent ingress or egress. In most cases, a door's interior matches its exterior side. But in other cases (e.g., a vehicle door) the two sides are radically different.