1. In terrestrial magnetism, the angle through which a freely suspended magnet would dip below the horizon in the magnetic north–south meridional plane; one of the magnetic elements. At the aclinic line (dip equator) the inclination is zero; at either magnetic pole (dip pole) the inclination is 90°. 2. The angle between the plane of the satellite orbit and the earth's equatorial plane. An inclination angle of less than 90° is referred to as a prograde orbit, while an inclination angle greater than 90° is called a retrograde orbit.