Gyroscope
From Virtual Reality, Augmented Reality Wiki
Gyroscope is a device that utilizes the gravity of earth to indicate the object's orientation. It consists of a freely-rotating disk mounted onto the center of larger wheels. The spinning axis of the disk is free to assume any orientation. When spinning, orientation of the disk is unaffected by any tilting or change in orientation of the outer wheels.
Gyroscopes in electronic devices are tiny MEMS versions that are part of the integrated circuit.
In virtual and augmented reality, gyrscopes are often part of IMUs used for rotational tracking. They are used to track the rotational movements of pitch, yaw, and roll.