Definition
Referenced to the Earth's magnetic field rather than to true (geographic) north. A magnetic direction is measured from magnetic north, which differs from true north by an angle called magnetic variation that changes with location.
Plain English
Measured using a magnetic compass and the Earth's magnetic field, not using the actual North Pole on a map. Because the magnetic pole and the geographic pole are in different places, a magnetic heading and a true heading are not the same number.
Context Anchor
Seen with headings, courses, bearings, runways, and wind directions used for navigation and air traffic control.
Derivation
From Latin magneticum, relating to the lodestone -- a naturally magnetised rock that early navigators used to find direction. The word still points back to that idea: a direction taken from a compass needle, not from a map's true north.
Why Pilots Care
Pilots must convert between magnetic and true directions using local variation to avoid navigation errors.
Intuition Check
Magnetic does not just mean something is attracted to a magnet. In aviation directions, it means the direction is referenced to the compass direction of magnetic north.
Example Sentence 1
Tower cleared us to fly a heading of 270 magnetic until intercepting the final approach course.
Example Sentence 2
Sectional charts show magnetic courses that already incorporate local variation.