What is Casing?

Definition of Casing in Construction
Term used to describe the trim around a door, window or opening on the interior of exterior of a structure. To case an opening, is to apply finish material around the opening, to close in the structural framing around the opening, and provide an architecturally finished door, window or simple opening. If the opening is for a door, then it is a door casing, a window, then it is a window casing. Normally the term is used to include all the pieces of the trim package used to enclose the sides, top and in some cases, the sill of the opening.