High Quality Content by WIKIPEDIA articles! A registered jack (RJ) is a standardized physical network interface — both jack construction and wiring pattern — for connecting telecommunications or data equipment to a service provided by a local exchange carrier or long distance carrier. The standard designs for these connectors and their wiring are named RJ11, RJ14, RJ21, RJ48, etc. Many of these interface standards are commonly used in North America, though some interfaces are used world-wide.