Bifolding doors outside were initially called folding patio doors. They were also known as folding bifold patio doors and bifold patio doors. Manufacturers and consumers have only recently adopted bifold doors as the generic name. Bifold doors can have as few as 2 doors or as many doors as necessary, depending on the size of your opening. They are usually joined with a specially constructed framework that allows them to fold and slide together quickly. Although it is possible to have 6 doors, this is not common.