Definition
The direction the airplane's nose is pointing, measured in degrees clockwise from magnetic north. It is true heading corrected for magnetic variation but not yet corrected for compass deviation.
Plain English
The direction your nose is pointing, measured against magnetic north rather than the geographic North Pole.
Context Anchor
Used during straight flight, navigation, and heading control when a pilot holds or turns to a compass-based direction.
Derivation
Magnetic' refers to Earth's magnetic field, which is what a compass actually senses. Magnetic north and the geographic (true) North Pole are not in the same place, so a heading based on the magnetic field will differ from one based on the true pole.
Why Pilots Care
Navigation aids and charts are aligned to magnetic north, allowing pilots to fly published courses directly without applying variation corrections in the cockpit.
Intuition Check
Magnetic heading is not the same as the path the airplane makes over the ground. It is where the nose is pointed, measured from magnetic north.
Example Sentence 1
After turning onto final, the pilot noted a magnetic heading of 270 degrees, lined up with the runway.
Example Sentence 2
Small corrections were made to maintain the assigned magnetic heading during the cross-country leg.