Is normally any given length of insulated magnet wire wound on a coil form or bobbin to a desired number of turns. A coil has a desired number of turns per layer and number of layers when wound on automatic traverse control winding machines. Scatter or hand winding will give you a coil with undetermined number of turns per layer and undetermined number of layers. Some coils can use no bobbin and are called an air coil that can be wound on a collapsible mandrel or winding fixture. Usually air coils are wound, potted and carefully taped to make handling much easier and safer.

Coils can be wound with numerous types of magnet wire insulation and gauges. Typical coils used in guitar and bass pickups can range from 35 AWG for lower impedance pickups to 46 AWG for special coils with space restrictions. The 46 AWG (American wire gauge) is much finer that 42 AWG which is commonly used in many guitar and bass pickups. If one turn is broken in a coil it will not work properly.