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.
The sliding glass door was introduced as a significant element of pre-war International style architecture in Europe and North America. Their precedent is the sliding Shōji and Fusuma panel door in traditional Japanese architecture. The post-war building boom in modernist and Mid-century modern styles, and on to suburban ranch-style tract houses, multi-unit housing, and hotel-motel chains has made them a standard element in residential and hospitality building construction in many regions and countries.