A prehung door is a door that comes with the door and hinges already installed in a frame. The frame includes the door jambs, or legs (the vertical elements), and the head jamb (the horizontal element) . The door slab is already hung in the frame and pre-cut for the doorknob and the strike plate. Prehung doors are recommended for rough door openings and exterior doors because they are easier to fit and come weathertight from the factory. They are also a convenient option that is relatively easy to install, as there is no need to build a frame, pre-cut a hole for the strike plate, or mortise the hinges, as all of those elements are provided by the manufacturer. Prehung doors may be shipped disassembled for ease of transportation.
In contrast, a slab door is a piece of wood that does not have hardware or hinges. Slab doors often do not have a cutout for the hardware or hinges. These doors can be used to replace an existing door in a frame that is still in good condition.
