- Electric circuits include resistors, capacitors, inductors, etc. A piece of wire has a very small amount of inductance, but usually we talk about inductors when we think about coils, which are a lot of wire wound in near-circles around a core which is some kind of magnetic material, such as iron. That core magnifies the inductance of the coil.
- While the wire has some resistance, the coil has not only that resistance, but also reactance. Reactance is proportional to frequency, and coils are used mainly in AC circuits for that reason. Usually the reactance(L) (in Ohms) is much higher than the resistance(R) of the inductor (also in Ohms), with the L/R ratio being important.
There is a limit to the strength of the magnetic field of an inductor, and therefore also a limit to the inductance of the inductor. Saturation is reached when a small increase in the electric current creating the magnetic field no longer causes an increase in the magnitude of the magnetic field. This is done intentionally in "Saturable reactors".