Which type of door incorporates a stop directly built into its frame?

The correct answer is a rabbetted door, which features a stop built directly into its frame. This design includes a rabbeted edge that creates a recess for the door to sit within the frame, ensuring a tight seal when closed. The built-in stop helps to prevent the door from swinging too far open or closed, providing better insulation and security.

In contrast, a slab door is a flat panel without any fittings or frames incorporated and relies on other components for closure. A ledge door is typically used in barns and sheds and features horizontal ledges for support but does not have an incorporated stop. A folding door is designed to collapse or fold into itself and does not have a stop built into the frame, as it operates on a different mechanism. This makes the rabbetted door unique among the options, as its design specifically addresses the need for a built-in frame stop.