A series of connectors generally used for phone wires
, or anything else using twisted pair copper wire
s. Typically they are made out of clear plastic. They have six sides. The wire trails out the back. The top includes a small tab to lock it in place in a female connector. The front/bottom corner and bottom side contains 4,6 or 8 gold fingers depressed in the plastic, running front to back. These make contact with the female connector's wires when put in place. Any RJ connector may fit into a female connector of a bigger size and still be held in place. They are listed below in decreasing size order (it is the width that varies between connectors).
RJ-45 - mainly networking
RJ-11 - mainly phone wires
RJ-12 - mainly cheap phone wires