The oldest and most generic term to describe this group of products characterized by groups of paired sashes or leaves (the moving parts of a door or window vs. the frame that attaches permanently to the building) is probably “bi-fold door”.
The hyphen is used originally to join words or add prefixes to words as in bi meaning two and fold or folding meaning to bend like taking a piece of paper and “folding” it in half. Over time the hyphen is often dropped forming a specific word like bifold or bifolding that has a single unifying meaning. Both forms, with and without the hyphen, area acceptable in most dictionaries. Therefore, bi-fold, bifold, bi-folding and bifolding all have the same meaning when used to describe a specific door type as discussed above. I prefer the hyphenated version mostly because I am old and that was the preferred form when I was growing up.
If you tell people that you make folding doors, altogether too many people assume you make closet doors. Millions of homes across America have homes with bi-folding closet doors in every bedroom . . . they are everywhere in numbers hundreds of times greater than exterior glass doors with similar functions. I recently drove five hours for a meeting where the designer was excited to meet me to talk about closet doors. This common usage could send people on a wild goose chase when trying to research bi-folding doors.
To avoid some of the confusion with the spelling of bi-fold some manufacturers have taken to calling these doors simply folding doors. No more spelling conundrum, and I kind of like the term personally. Nevertheless, this simple term, folding, does not avoid the need for a longer description to make sure that speaker and listener are on the same page.
Folding doors that are NOT bi-folding would be the accordion plastic or plastic room partitions or closet doors that had pleats that folded up both to the inside and outside. This kind of door is still commonly used in RV’s and mobile homes. If we are thinking about these terms within the context of mostly glass, exterior doors, folding is just a simplified form to describe bi-fold doors.
Movable glass wall is the newest incarnation to describe exterior glass bi-folding doors to change the focus away from its opening potential and focus on the image that it is first and foremost a glass wall that can also fully open. One could also describe sliding doors as movable glass walls. Sliding doors are the biggest outside competitor to bi-fold doors in function and producers of each have arguments against the other. Sliders stop looking like walls when they get very wide and the offset glass panes of each sash create a very wide sill track and the light reflects oddly. Also, unless the sliding panels go into or behind the wall, the stack of panels only create a partial opening. Bi-fold doors have all the glass on one thin plane within a normal wall thickness and are therefore more wall-like.
All arrogance aside, I decided to stay close to original term of bi-folding door and invented the term 2Fold® to describe our product offering. By substituting the “2” for the “bi” and leaving the hyphen out the confusion is avoided. Aren’t I the clever one. So, if you are looking for a movable glass wall with multiple panels that look like the most beautiful fixed glass wall you have ever seen and has (bi) folding panels that gather to the ends creating a clear opening from inside to outside, check out our website or give me a call. Forget the other terms, get a 2Fold®