Voltage is the difference of electrical potential between two points of an electrical or electronic circuit, uttered in volts. It measures the potential energy of an electric field to source an electric current in an electrical conductor. Depending on the difference of electrical potential it is called extra low voltage, low voltage, high voltage or extra high voltage.
Between two points in an electric field, such as exists in an electrical circuit, the distinction in their electrical potentials is known as the electrical potential difference. This difference is proportional to the electrostatic force that tends to drive electrons or other charge-carriers from one point to the other. Potential difference, electrical potential, and electromotive force are measured in volts, leading to the commonly used term voltage. Voltage is usually represented in equations by the symbols V, U, or E.
Electrical potential difference can be thought of as the capacity to move electrical charge through a resistance. At a time in physics when the word force was used loosely, the potential difference was named the electromotive force or EMF—a term which is still used in confident contexts.