Voltage
The electric potential difference between two points, defined as the work required per unit charge to move a positive test charge between them.
Governing formula
V = W / q = I R
SI unit
V (Volts = J/C)
In depth
Voltage acts as the electrical pressure that drives current through a circuit. One Volt represents one Joule of energy expended per Coulomb of charge transferred. In an electric circuit, current flows spontaneously from higher potential to lower potential.
Examples in the real world
A standard 1.5 V AA alkaline battery, a 12 V automotive battery powering starter motors, or 120 V AC household wall outlets.