Definition
Directional gyros that are continuously corrected (slaved) to magnetic north by signals from a remote magnetic sensor, typically a flux gate or flux valve mounted in the wingtip or tail. The slaving system uses these magnetic reference signals to keep the gyro's heading indication aligned with magnetic north, automatically correcting for the precession (gradual drift) that affects all mechanical gyros.
Plain English
A heading gyro that is automatically kept pointing the right way by a magnetic sensor mounted somewhere quiet on the aircraft. The pilot doesn't have to keep manually resetting it because the system corrects it on its own.
Context Anchor
Seen in instrument-panel heading systems that use a flux gate compass to keep the displayed heading corrected during flight.
Derivation
Slaved' here is an engineering term meaning 'controlled by, or made to follow, another device.' One unit (the gyro) is made to follow the reference signal from another (the magnetic sensor). The everyday meaning of 'slave' is not the meaning intended -- it's purely a technical word for one device taking its cue from another.
Why Pilots Care
Reduces the need for frequent manual heading resets and provides reliable directional information during instrument flight.
Grounding Statement
The gyro gives a steady direction reference, and the magnetic compass sensor keeps nudging it back into correct alignment.
Intuition Check
Slaved does not mean manually controlled by the pilot. Here it means the gyro is automatically made to follow another device’s heading signal.
Example Sentence 1
Because the heading indicator uses slaved gyros, the pilot didn't need to reset it against the magnetic compass during the cross-country flight.
Example Sentence 2
During preflight the crew confirmed the slaved gyro was receiving valid signals from the flux gate compass.