Here is a good quick refresher on voltage from wikipedia:

Voltage, electric potential difference, electric pressure or electric tension (denoted ∆V or ∆U) is the difference in electric potential energy between two points per unit electric charge. The voltage difference between two points is equal to the work done perunit of charge against a static electric field to move the charge between two points and is measured in units of volts (a joule percoulomb).

Voltage can be caused by static electric fields, by electric current through a magnetic field, by time-varying magnetic fields, or some combination of these three. A voltmeter can be used to measure the voltage (or potential difference) between two points in a system; often a common reference potential such as the ground of the system is used as one of the points. A voltage may represent either a source of energy (electromotive force), or lost, used, or stored energy.

We hope you like the video!