The term voltage is used to quantify the pressure or force pushing electrons through a conductor. For electrons to move from atom to atom, there must first be a force. Voltage is measured in units of volts, kilovolts, and megavolts.
Consider a water piping system as an analogy to an electrical circuit. Force or pressure must be applied to the water to get it to move through the pipe. The same is required in an electrical system. In order to get the electrons to move, an electrical pump is required to provide the force, or voltage, to make the electrons flow. The device that provides this electrical pressure is called a generator.
There are two symbols commonly used to designate voltage, E and V. While the symbol V is intuitive, the symbol E may be confusing. In the early days of the electric industry, voltage was known as an electromotive force, and thus abbreviated with an E. The acceptable voltage at any point in the electrical system is dictated by various industry standards and must always be carefully managed on the transmission and distribution system. Too much voltage can destroy electrical equipment just as putting too much water pressure on a plastic pipe can cause it to break. Too little voltage will not destroy electrical equipment but will cause it to operate incorrectly.
Voltage can be increased or decreased at various points throughout the system using transformers, capacitors, and reactors.