The magnetic meridian refers to a plane that passes through the magnetic north and magnetic south of the Earth. It is important to note that the Earth has both geographic poles (north and south) and magnetic poles (north and south). The magnetic poles do not align exactly with the geographic poles.

Option 1 is incorrect because the magnetic meridian is not parallel to the equator of the Earth. The equator is a circle that is perpendicular to the axis of rotation of the Earth.

Option 2 is incorrect because latitude refers to horizontal lines that measure the distance north or south of the equator.

Option 3 is incorrect because the magnetic meridian does not necessarily align with the geographic north and geographic south of the Earth.

Therefore, option 4 is the correct answer, as it accurately describes the magnetic meridian as a plane passing through the magnetic north and magnetic south of the Earth.