What characteristic defines a rabbeted door jamb?

A rabbeted door jamb is characterized by having a shoulder milled into the door casing. This shoulder allows the door to fit snugly into the jamb, providing better alignment and sealing when the door is closed. The rabbet itself refers to the recess or groove cut into the edge of the jamb that accommodates the edge of the door, which helps to reduce air and water infiltration. This feature is particularly important for enhancing the overall efficiency and security of the door.

In contrast, the other options do not accurately capture the defining feature of a rabbeted door jamb. While a flat surface may aid in installation, it is not a defining characteristic of a rabbeted design. Round door knobs can be fitted in various door jamb styles, not specifically rabbeted ones. Finally, although hollow metal door jambs exist, the material does not define all rabbeted jambs, which can also be found in wood or solid metal formats. Thus, the key defining feature remains the shoulder milled into the casing, which securely supports the door.