The axis of rotation is called a relatively stationary straight line around which a rigid body rotates. In this case, a necessary condition is that at least 2 points of the body must be motionless. Interestingly, the axis of rotation may not pass through the body, but be located outside of it. The axis may or may not be movable. A good visual example is the rotation of our planet around its axis, and in a reduced form this is illustrated by the globe.
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