What is the angular difference between true north and magnetic north known as?

The angular difference between true north and magnetic north is referred to as magnetic variation. This term is essential for navigation because it quantifies how much a magnetic compass will deviate from true north due to the Earth's magnetic field. Magnetic variation is expressed in degrees and can vary by location and time, making it crucial for pilots and navigators to be aware of it when interpreting compass readings and when aligning their flight path with true heading. Understanding magnetic variation is vital for accurate navigation, as it ensures that pilots can adjust for this difference when using compasses, thus improving their situational awareness and flight accuracy.