Butt doors are a pair of doors that open from the center and close towards each other. They refer specifically to a set of double doors that do not have a center stile between the doors.

Butt doors have a symmetry to them that looks pleasant to the eye. The gap between the doors is narrow, about 1/8 of an inch, to allow both sides to open. By having smaller doors that you can access from the middle, rather than a large door opened from one side, you don’t need to worry as much about clearance for the door to open fully.