Bi-Fold Doors/Windows are two doors/windows hinged together that fold into one another. They are mounted on a track that hangs from the top of the opening. An opening can hold one single bi-fold door/window or two doors/windows that meet in the middle. They are a popular choice because when they are opened, there is less intrusion into the room than standard doors/windows.

The design of bi-fold doors/windows can be solid, louvered, or a combination of both. There are also six-paneled bi-fold doors for added design. Bi-fold doors/windows are generally not used for areas requiring privacy, such as bathrooms.

WIKIPEDIA ENTRY FOR DOOR.