= What does 's' denote in describing a General Linear Model (GLM)? =

The GLM terminlogy is described [http://www.fil.ion.ucl.ac.uk/~mgray/ here] in relation to using SPM.

Examples of GLMs include linear regressions and analysis of variance and are of form.

{{{
Y = XB + error
or, in words,
Response = Prediction + residual
}}}

The term s is the residual standard deviation which, for example, corresponds to the square root of the mean square error term in an analysis of variance.