The Fit Mean report shows summary statistics about the fit of the mean.
Mean
Mean of the response variable. The predicted response when there are no specified effects in the model.
Std Dev [RMSE]
Standard deviation of the response variable. Square root of the mean square error, also called the root mean square error (or RMSE).
Std Error
Standard deviation of the response mean. Calculated by dividing the RMSE by the square root of the number of values.
SSE
Error sum of squares for the simple mean model. Appears as the sum of squares for Error in the analysis of variance tables for each model fit.
For more information about the options in the Fit Mean menu, see Fitting Menus.