Radius of gyration or gyradius refers to the distribution of the components of an object around an axis. In terms of mass moment of inertia, it is the perpendicular distance from the axis of rotation to a point mass (of mass, m) that gives an equivalent inertia to the original object(s) (of mass, m). The nature of the object does not affect the concept, which applies equally to a surface, a bulk mass, or an ensemble of points.