A Gyroscope is a device used for measuring or maintaining orientation and angular velocity. The simplest form of gyroscope (or gyro) consists of a rapidly spinning disc (called a rotor). The shaft about which the rotor spins is called the axis. Gyros have its mass evenly distributed around its spin axis and are defined in their orientation as either horizontal or vertical by reference to the spin axis, not the rotor.

In order for a gyro to be able to maintain a fixed direction, it must be attached to the airframe in such a way that the aircraft has freedom to manoeuvre without disturbing the orientation of the gyro. This is achieved by using suspension devices which allow this freedom. These are called gimbals. Gyros may have one or two gimbals.