What term describes the difference between magnetic north and true north?

The term that describes the difference between magnetic north and true north is known as variation. Variation, also referred to as magnetic declination, is the angle between the magnetic compass direction and the true direction (geographic north). This discrepancy arises because of the Earth's magnetic field's irregularities, which can cause the magnetic north to differ from the geographic north.

Understanding variation is essential for navigation, as it allows mariners to correct their compass readings when plotting their courses. The variation can change depending on the geographic location and can also shift over time due to changes in the Earth's magnetic field.

The other terms listed do not fit this definition. Deviation refers to the error introduced in a compass reading by local magnetic fields, Magnetic Drift pertains to the gradual shift in the magnetic poles over time, and Azimuth is a term used to describe an angular measurement in a spherical coordinate system.