Statistical Glossary
Quadratic Mean:
The quadratic mean is a special case of the power mean statistics 
, corresponding to the value 
of the parameter. The quadratic mean is a synonym of root mean square .
The quadratic mean is used as a measure of "effective magnitude" of a set of non-negative values. This measure is scale invariant but not shift invariant .
See also: mean values (comparison) and the online short course Basic Concepts in Probability and Statistics