Voltage is an electric charge, or potential, between two points, one being of higher relative voltage than the other is. A 1.5-volt battery has 1.5 volts of differential between the positive and negative end, for example. The unit of voltage is called the “volt,” named after Allesandro Volta. Voltage can be thought of metaphorically as a pressure, such as water pressure in plumbing, that is available to initiate action or work. It, however, cannot do any work until a circuit is complete so that current (measured in amperes) can flow.