Voltage is defined as the potential difference between two points of a conducting wire. It is used to measure EMF or potential difference. A volt is the amount of potential necessary to cause 1 coulomb to produce 1 joule of work.
Voltage is the force that pushes the electrons through a wire and is often referred to as electrical pressure. It is important to remember that voltage does not flow. It is the pressure that causes the electrons to flow, or the pressure that causes current.
Current is directly proportional to the voltage. If the voltage goes up, the current goes up and vice versa. Voltage must be present in order for current to flow.
The symbol E or V is used for voltage.