A standard for signal interconnections, widely used in synthesizers and particularly modular synthesizers. The phone jack standard was, as the name suggests, originally developed for use in telephone switchboards. The male jack is cylindrical with a pointed tip and a grooved band near the tip; it has an insulator that separates the tip area from the barrel of the cylinder (referred to as the "sleeve"). In use, interconnection cords or patch cords always have male connectors at both ends, and the equipment being connected always has female connectors.