Error term in a repeated measures design?

What is the error term in a repeated measures design?

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The inconsistent individual differences across conditions, the effect of subjects that differ across conditions. So it is an interaction between subjects and condition.
The unsystematic variance that is reduced as a function of the systematic between-groups variance. So if the variable conditions just reveals stable individual differences across an experiment then that can be contributed to conditions and that gets taken out of the error term.
The error term represents the interaction between subjects and IQ; it is the effect of IQ that differs across subjects.