A stile is any vertical piece in frames such as doors and windows; it joins to the horizontal rails. Stiles and rails are the joiners equivalent of the carpenter's posts and beams. Note that the words "post and beam" have Old English origins, while "stile and rail" have French-Latin origins, which lets you know who got the indoor work after the Norman invasion. Panels fill the space between frames, riding freely in grooves plowed inside the perimeter of the frames. By their free expansion and contraction within these grooves, panels fill the open space, respond to changes in humidity, and never open a crack. A rail is the horizontal piece in frame construction, supported by the vertical stiles. In a panel door, one would find the top rail, the bottom rail, and, midway between them, the lock rail (where the door lock goes). Windows have top and bottom rails, with muntins in between.