The sum of squared deviations of individual measurements from the mean. The total sum of squares is a sum of 2 portions; regression sum of squares and error sum of squares
The sum total of a number of things is all the things added or considered together. You often use this expression to indicate that you are disappointed because the total amount is rather small. That small room contained the sum total of the family's possessions = sum. the whole of an amount the sum total of