(Registered Jack-11) A telephone interface that uses a cable of twisted wire pairs and a modular jack with two, four or six contacts. RJ-11 is the common connector for plugging a telephone into the wall and the handset into the telephone. See modular connector. RJ-11, 14, 25 - One, Two and Three Lines RJ-11 cables can hold six wires for up to three telephone lines, and their nomenclature is technically RJ-11, RJ-14 or RJ-25 depending on the number of lines (see chart below). RJ-21X, RJ-26X and RJ-27X For PBX and other telecom connections, RJ-21X, 26X and 27X cables use a 50-pin Centronics-style "Miniature Ribbon" connector to handle 25 telephone lines in one cable. C and W The C refers to a desk phone jack, such as RJ-11C, while RJ-11W means a wall-mounted jack. See modular connector.