Voltage is a measure of energy, its the energy carried by electrical charge. The voltage between two points in a circuit is the amount of energy available for pushing each charge from one of these points to the other.

Voltage is created when something with an electrical charge makes a circuit. In order for a circuit to be created the voltage must be able to flow through the object creating the circuit. The object that it flows through would be called a conductor. If the voltage cannot pass through the object to create a circuit then the object would be an insulator. An insulator has more resistance to electricity then the charge is trying to push.