ISO 1940 defines Unbalance as condition which exists in a rotor when vibration force or motion is imparted to its bearings as a result of centrifugal forces” or in simple terms it’s the “Uneven distribution of mass”.

Balancing is the process of adjusting the mass distribution and is defined as “the procedure by which the mass distribution of a rotor is checked and, if necessary, adjusted to ensure that the residual unbalance or the vibration of the journals and/or forces on the bearings at a frequency corresponding to service speed are within specified limits”.