Patio doors refer to a type of sliding glass door that leads from an interior space, such as a living room or dining area, onto an outdoor patio or balcony. These doors provide easy access between the indoor and outdoor spaces while allowing for plenty of natural light to enter the room. They are typically made up of two or more large panes of glass that slide horizontally on a track system, allowing them to open wide when needed. Patio doors can be opened completely, creating an unobstructed view between the indoor and outdoor spaces, making it perfect for entertaining guests or simply enjoying the fresh air.