A gyroscope is a device that consists of a spinning mass, usually a heavy disk called a rotor, that is mounted on a base with a spin axis positioned through the center of the rotor. The rotor can turn freely in any direction, which are commonly called "pitch", "roll", and "yaw". The rotor is mounted and moves within gimbals within a frame and maintains its orientation regardless of any movement of the base.
The rotor and the spin axis will remain in their original position and perpendicular to each other even if the base moves.
In aviation, attitude indicators and the heading indicators use gyroscopic properties for their operation.
Gyroscopes played an important part in creating the gyrocompass, a compass that finds true north (the direction of Earth's rotational axis) and is not negatively influenced by ferrous metal in the ship's hull.
Gyroscopes were originally used to provide attitude reference points for inertial navigation system. However modern INS will more typically use a laser gyroscope, which, despite it's name, does not use gyroscopic principles at all.