A sliding door is a type of door which opens horizontally by sliding, usually horizontal to a wall. Sliding doors can be mounted either on top of a track below or be suspended from a track above. Some types slide into a space in the parallel wall in the direction of travel, rather than the door sliding along the outside of the parallel wall.[1] There are several types of sliding doors, such as pocket doors, sliding glass doors, center-opening doors, and bypass doors. Sliding doors are commonly used as shower doors, glass doors, screen doors, wardrobe doors or in vans.