Door that opens and closes by sliding sideways instead of by swinging on hinges. A sliding glass door or patio door, is a type of sliding door in architecture and construction, is a large glass window opening in a structure that provide door access from a room to the outdoors, fresh air, and copious natural light. A sliding glass door is usually considered a single unit consisting of two panel sections, one being fixed and one a being mobile to slide open. Another design, a wall sized glass pocket door has one or more panels movable and sliding into wall pockets, completely disappearing for a 'wide open' indoor-outdoor room experience.