Inductance, also called self-inductance, is the amount of magnetic flux (Φ) produced for a given electric current (I). Inductance L = Φ / I. Another way of saying this is that inductance is the ratio of the voltage induced (see electromagnetic induction) to the rate of change of the current. It depends on the circuit geometry, being large for coils and small for extended circuits, and is greatly increased by the presence of ferromagnetic materials.
Voltages induced by currents in a different circuit are measured in terms of mutual inductance. Inductors have an impedance to AC circuits proportional to the current, and are widely used in electronics.