Plain English Meaning
A set of pivoting rings that hold the spinning wheel inside a gyro instrument. They let the wheel keep pointing the same way even when the aircraft tips or turns around it.
Full Definition
The pivoted support frames that suspend a gyroscope's spinning rotor so it can remain free to maintain its orientation while the aircraft moves around it. In a typical gyroscopic instrument, two gimbal rings are mounted at right angles to each other, allowing the rotor to remain undisturbed as the airframe pitches, rolls, or yaws.
Context Anchor
Seen in discussions of gyroscopic instruments, such as attitude indicators and heading indicators.
Derivation
From the French 'cardan' and earlier Italian 'gimbale', referring to the pivoted rings used in old ship compasses to keep them at sea. Knowing this helps because the job is the same in an aircraft: the rings isolate the spinning element from the motion of the vehicle around it.