Root-Mean-Square Deviation (RMSD)

of an estimator of a parameter[; ...] the square-root of the mean squared error (MSE) of the estimator. In symbols, if X is an estimator of the parameter t, then RMSE(X) = ( E( (X−t)2 ) )½. The RMSE of an estimator is a measure of the expected error of the estimator. The units of RMSE are the same as the units of the estimator.

a frequently used measure of the differences between values (sample or population values) predicted by a model or an estimator and the values observed