Inductor
Coil, measured in henries (H)
An inductor is a coil of wire that resists changes in current by storing energy in a magnetic field.
Inductors are in power supplies, radios, motors and relays (every relay coil is one).
When the current through a coil is switched off suddenly, it kicks back a high voltage. That's why relays and motors need a flyback diode.
Everything on this subject: Capacitors, Simplified