Air gap

[1] The space bet magnetic poles or between rotating and stationary assemblies in a motor or generator
[2] Usually found on regulators, it is the distance between the contact armature and the iron core that when magnetized, draws the armature down.
[3] It is also the distance between the two electrodes of a spark plug.
See also spark air gap
[4] Gap with points or knobs, adjusted to breakdown at a specified voltage and hence limit voltages to this value.
[5] Section of air, usually short, in a magnetic circuit, esp. in a motor or generator, a relay, or a choke. The main flux passes through the gap, with leakage outside depending on dimensions and permeability.