Casement window, earliest form of movable window, wood or metal framed, with hinges or pivots at the upright side of the vertically hung sash, so that it opens outward or inward along its entire length in the manner of a door. One frame, separately movable, of such a window is called a casement sash. Casement doors are offered as a single sash creating a beautiful main entrance or as dual sash, also referred to as French doors, connecting the indoors with the outdoors. These versatile doors can be used for patio, deck or balcony access.Many people find that a casement window adds a clean modern style, especially since they don’t have the sash dividing the window like a double-hung window does