Voltage is a physical quantity that characterizes the potential difference between two points in an electric field and indicates how much work is required to move a unit charge from one point to another:
$$U = \frac{A}{q}$$
where,
A— work done by the electric field to move the charge;
q— charge.
The unit of voltage in the SI system is volt (V). Voltage is 1V when an electric field does 1 joule (1J) of work in moving one coulomb (1C).