Voltage is the electrical equivalent of mechanical potential. If a person drops a rock from the first storey of a building, the velocity it will reach when dropped will be fairly small. However, if the rock is dropped from the twentieth floor, it will have reached a much greater velocity on reaching the ground. On the twentieth floor the rock had much more potential energy.
The potential energy of an electrical supply is given by its voltage. The greater the voltage of a supply source, the greater its potential to produce a current flow. Thus, a 115 volt supply has 115 times the potential to produce a current flow than a 1 volt supply.
If one coulomb of electrons is added to a body and one joule of work has been done, then the body will acquire of potential of - 1 volt. If the electrons had been removed, then the body would have acquired a potential of +1 volt. The unit of potential is the volt.