What does the term variation refer to in navigation?

Variation refers specifically to the difference between True North and Magnetic North. In aviation and navigation, understanding this difference is crucial for accurately determining the aircraft's heading and ensuring it aligns with the magnetic compass. True North refers to the geographic North Pole, while Magnetic North is where the Earth's magnetic field points vertically downwards.

This discrepancy exists because the Earth's magnetic field is not uniform and varies in magnitude and direction at different locations on the surface. Pilots need to apply this variation when converting between true headings and magnetic headings, which helps in chart navigation and aids in maintaining the intended flight path.

The other choices pertain to different aspects of navigation and flight. GPS inaccuracies are related to the technology used for navigation rather than the magnetic fields in the Earth. Wind speed, while a significant factor in flight dynamics, does not relate to the concept of variation. Changes in altitude are essential for aircraft performance and safety but do not directly impact the understanding of directional navigation.