It is defined as the ratio of magnetomotive force (mmf) to magnetic flux.

It represents the opposition to magnetic flux, and depends on the geometry and composition of an object.

The definition of magnetic reluctance is analogous to Ohm's law in this respect.

However, magnetic flux passing through a reluctance does not give rise to dissipation of heat as it does for current through a resistance.

[1] The notion of "magnetic resistance" was first mentioned by James Joule in 1840.

[2] The idea for a magnetic flux law, similar to Ohm's law for closed electric circuits, is attributed to Henry Augustus Rowland in an 1873 paper.

In both AC and DC fields, the reluctance is the ratio of the magnetomotive force (MMF) in a magnetic circuit to the magnetic flux in this circuit.

The concentration of flux in low-reluctance materials forms strong temporary poles and causes mechanical forces that tend to move the materials towards regions of higher flux so it is always an attractive force (pull).