Casing is the trim board that frames a door or window and covers the gap between the frame and the drywall. This one is the Contemporary style: flat and simple, with a stepped slope along one edge and no carved detail. Made from MDF, which stands for medium density fibreboard: a smooth engineered wood board with no grain and no knots, so it takes paint well.

• What it is: One piece of casing, 14 ft long, sold by the piece.
• Size: 3/4" thick by 2-3/4" wide.
• Profile (the shape the edges are cut to): A flat face with a small step, then a straight slope down to the thinner edge. The other long edge is thicker and square. Install it with the thinner edge against the door frame (or the window frame, if you are casing a window) and the thicker edge out on the wall.
• Finish: Primed white, so a base coat is already on and it is ready for your paint.
• How many pieces: Casing goes on both faces of the wall around a doorway. Each face takes two uprights of about 84 in and one header across the top, so a standard door uses four uprights and two headers. Three 14 ft pieces cover a standard door with some left over, about 1.5 pieces per face. Measure your opening before you order.
• About the photo: we picked an image that matches this trim as closely as we could, so it is a close look at the shape and finish. It is not a photo of the exact piece you receive, and the proportions can differ a little from the real thing, especially between sizes.