A line connecting all points on the earth's surface at which a magnetic needle balances horizontally without dipping.
An imaginary line around the earth near the equator, where the lines of force of the earth's magnetic field are parallel with the surface of the earth and where a magnetic needle will consequently not dip.
A line connecting all points on the earth's surface at which the magnetic field is parallel to the Earth's surface. A balanced magnetic needle on the magnetic equator stabilizes in a perfectly horizontal position.
(military) A line drawn on a map or chart connecting all points at which the magnetic inclination (dip) is zero for a specified epoch.