From Glossary of Meteorology


The direction of a line over the earth with reference to north (true or magnetic).

Because the meridian lines converge at the poles, the true course of a line changes continuously except when it is actually meridional or when it is curved so as always to cross meridians at the same angle. Magnetic course also changes but in a nonuniform manner because of the lack of complete symmetry in the isogonic lines of the earth's magnetic field.
Compare heading.