What do you understand by reluctance?

In a DC field, the reluctance is the ratio of the "magnetomotive force” (MMF) in a magnetic circuit to the magnetic flux in this circuit. In a pulsating DC or AC field, the reluctance is the ratio of the amplitude of the "magnetomotive force” (MMF) in a magnetic circuit to the amplitude of the magnetic flux in this circuit.. (see phasors)

The definition can be expressed as follows:

where

("R") is the reluctance in ampere-turns per weber (a unit that is equivalent to turns per henry). "Turns" refers to the winding number of an electrical conductor comprising an inductor.

("F") is the magnetomotive force (MMF) in ampere-turns

F ("Phi") is the magnetic flux in webers.

It is sometimes known as Hopkinson's law and is analogous to Ohm's Law with resistance replaced by reluctance, voltage by MMF and current by magnetic flux.