Question

Define magnetic declination.

Answer 1

The magnetic field of earth is supposed to be a field by a bar magnet and this bar magnet is not along the

$Geographic$ $meridian$ of earth whereas it makes an angle to it in a horizontal plane.

In other words the $\text{Magnetic declination is the angle between geographic north and magnetic north(along the north pole}$

$\text{of a horizontal magnetic compass)}$