A casement window is one that has been attached to its frame by the use of one or more hinges. These windows are mostly hinged at the side. They can be used in pairs or singly within the same frame. When these windows use a common frame, they are hinged on the outside.
The windows are usually opened with lever, a crank or a cam handle that is placed around the bottom, or at hand height and usually serve as a window lock. A friction hinge, stay or crank is very necessary in cases when the window opens outward so that it is held in a stable position regardless of the wind. A rabbet frame is used to set the glass panes as a way of securing the glass.