What is referred to as the difference between true north and magnetic north?

The difference between true north and magnetic north is called magnetic variation, also commonly referred to as magnetic declination. This term describes how much your compass reading differs from true north, which is the direction along the Earth's surface towards the geographic North Pole.

Magnetic variation is essential for navigation because navigators must correct their compass readings to get accurate headings. This correction is necessary because the Earth's magnetic field does not align perfectly with its geographic axes; thus, magnetic north is not the same as true north. The value of magnetic variation can change depending on where you are on the Earth's surface and can also shift over time due to changes in the Earth's magnetic field.

Understanding magnetic variation is crucial for accurate navigation, especially in aviation and maritime operations, where precise headings are necessary for successful travel.