(Or "potential difference", "electro-motive force" (EMF)) A quantity measured as a signed difference between two points in an electrical circuit which, when divided by the resistance in Ohms between those points, gives the current flowing between those points in Amperes, according to Ohm's Law. Voltage is expressed as a signed number of Volts (V). The voltage gradient in Volts per metre is proportional to the force on a charge.
The voltage between two points is also given by the charge present between those points in Coulombs divided by the capacitance in Farads. The capacitance in turn depends on the dielectric constant of the insulators present.