A restrained gyro with one degree of freedom is often referred to as what?

A restrained gyro with one degree of freedom is often referred to as a rate-of-turn gyro because it is designed to measure the rate at which an aircraft is turning. This type of gyro is mounted in such a way that it is restricted from moving in more than one axis, allowing it to detect changes in orientation related specifically to turning motions. By measuring the rate of turn, this gyro provides important information to pilots about the aircraft's maneuvering capabilities and stability during flight.

In contrast, other types of gyros serve different purposes: a tilt gyro is used primarily for sensing changes in pitch and roll, a 3-D gyro can measure motion in multiple axes, and a directional gyro indicates the aircraft's heading but is not limited to just rate of turn measurement. Therefore, the classification of a restrained gyro specifically as a rate-of-turn gyro underscores its unique function in aviation navigation and control.