Reluctance

In physics and electronics reluctance is the measure of the degree to which a material will resist magnetic flux, or in simpler terms, the degree to which it will not take on or pass magnetic energy. Reluctance is therefore an important specification in any material designed to store information in the form of magnetic charges, such as audio or video tape, etc. End users will not frequently encounter this spec because it is one of many factors taken into consideration at the engineering and manufacturing stages that ultimately becomes part of the overall performance of some media. An audio engineer aligning an analog tape machine will know the reference fluxivity he/she is calibrating the machine to (for a particular type of tape being used), and this ultimately takes into consideration many factors, including reluctance.