The henry is the SI unit of inductance.
Inductance measures how strongly a circuit or component opposes changes in electric current by producing an induced voltage. One henry is the inductance that produces a voltage of one volt when the current changes at one ampere per second. The unit is written H.
The name honors Joseph Henry, an American scientist whose work on electromagnetic induction was contemporary with Michael Faraday’s. The two researchers independently discovered important aspects of induction in the 1830s. An inductor with greater inductance stores more energy in its magnetic field for a given current and more strongly resists rapid current changes.
A common mix-up is confusing the henry with the weber, the SI unit of magnetic flux, or the farad, the SI unit of capacitance. Inductors are commonly made from coils of wire, sometimes wound around magnetic cores that increase inductance.