Any of several reversals in the polarity of the Earth's magnetic field (such that a compass points South) that have happened over geologic time.

(physics) a measure of the magnetization of a material per unit of applied magnetic field

(physics) A measure of the strength of a magnetic field in a given area.

(military) A mine which responds to the magnetic field of a target.

(electromagnetism) A closed path of magnetic flux.

(nautical, navigation) Directional bearing relative to the nearest magnetic pole, as shown by a compass.

(military, nautical, navigation) In navigation, at a given place and time, the horizontal angle between the true north and magnetic north measured east or west according to whether magnetic north lies east or west of true north.

(military, nautical) An instrument containing a freely suspended magnetic element which displays the direction of the horizontal component of the Earth’s magnetic field at the point of observation.

The horizontal angle between magnetic north and true north at a given place.

(military) A line drawn on a map or chart connecting all points at which the magnetic inclination (dip) is zero for a specified epoch.