Volt

The volt is defined as:

$1\text{ V} = \frac{1\text{ J}}{1\text{ C}}$

One volt means one joule of energy is transferred for every coulomb of charge that passes.

A voltmeter measures potential difference and is connected in parallel across a component.

Typical voltages: AA battery 1.5 V, car battery 12 V, UK mains 230 V, overhead power lines 400 000 V.