The line of attractive force that runs through the center of the earth. The earth's magnetic axis differs slightly from its rotational axis.
The physical length of the magnet dimension which corresponds to the direction the magnet is magnetized. This may or may not be the magnet's orientation direction.
A meridian (or line of longitude) is the half of an imaginary great circle on the Earth's surface, terminated by the North Pole and the South Pole, connecting points of equal longitude. The position of a point along the meridian is given by its latitude. Each meridian is perpendicular to all circles of latitude. Each is also the same length, being half of a great circle on the Earth's surface and therefore measuring 20,003.93 km