Variance is also called MS, Mean Square; approximated by the sum of squares (SS) divided by the degrees of freedom (i.e., n-1); the MSE from the empty model can be thought of as roughly the average squared deviation.
A categorical variable is a variable that places observations into groups or categories. Instead of measuring “how much,” categorical variables describe “which kind.” Examples of Categorical Variables Variable Example Categories Eye color blue, ...
Confounding variable is a variable that, though not measured, causes variation in both the explanatory variable and the outcome variable; also know as a "lurking variable" or a "third variable".