Plain English Meaning
An instrument in the cockpit that shows which direction the airplane is pointing, using a small magnet that lines up with the Earth's magnetic field.
Full Definition
A self-contained navigation instrument that uses a magnetized element, suspended in a fluid-filled housing, to align with Earth's magnetic field and indicate the aircraft's heading relative to magnetic north.
Context Anchor
Seen during the visual preflight inspection and used in flight as a basic direction reference or backup to other direction instruments.