Voltage
Definition
The electrical 'push' — how much energy each unit of charge carries as it flows through a circuit.
Symbol: · Unit: volt (V)
Technical definition
Electric potential difference between two points: the work per unit charge needed to move charge between them, V = W/q. It is the driving influence behind current in a circuit.
Example
A 9 V battery gives every coulomb of charge 9 joules of energy to spend pushing through the circuit — which is why a 9 V battery lights a bulb far more brightly than a 1.5 V cell driving the same bulb.
Voltage is not current, and voltage alone does nothing. A 12 V car battery can deliver hundreds of amps (dangerous), while a 25,000 V Van de Graaff generator delivers microamps (a startling but harmless shock). What flows — and what heats, lights, and shocks — is current; voltage is just the push behind it.