1. The property of an electric circuit by which an electromotive force is induced in it as the result of a changing magnetic flux.
2. A circuit element, typically a conducting coil, in which electromotive force is generated by electromagnetic induction.
3. That property of a circuit or device by virtue of which any variation in the current flowing through it induces an electromotive force in the circuit itself (self-inductance) or in another conductor (mutual inductance). Without qualification, it is usually the former.

Also, the magnitude of this, as measured by the ratio of an induced electromotive force to the rate of change of the inducing current.

A number of turns of wire used to introduce inductance into an electric circuit, to produce magnetic flux, or to react mechanically to a changing magnetic flux.

In high-frequency circuits, a coil may be only a fraction of a turn.