Tip and ring

Tip and ring are the names of the two conductors or sides of a telephone line. The terms originate in reference to the telephone plugs used for connecting telephone calls in manual switchboards. One side of the line is connected to the metal tip of the plug, and the second is connected to a metal ring behind the tip, separated and insulated from the tip by a non-conducting material. When inserted into a jack, the plug's tip conductor connects first, followed the ring conductor. In many European countries tip and ring are referred to as the A and B wires.