What is the meaning of voltage?

Voltage is the difference of electrical potential between two points or two objects. Without this difference of electrical potential, electricity could not be used as a power source.

The number associated with voltage doesn't matter as much as the difference of voltage between two objects or points; this is because zero can be set at any arbitrary point. For example, 60 and -60 volts are the same amount, just oriented in opposite directions. The most common analogy used to describe voltage is that of water pressure building up in a garden hose. High voltage means high pressure, and current occurs when the potential energy is allowed to flow between the two points, similar to water coming from the hose.