volt [for Alessandro Volta], abbr. V, unit of electric potential and electromotive force. It is defined as the difference of electric potential existing across the ends of a conductor carrying a constant current of 1 ampere when the power dissipated is 1 watt. The kilovolt (1,000 V), the millivolt (0.001 V), and the microvolt (0.000001 V) are units derived from the volt. See voltmeter.