«Goals Saved Above Average is calculated by the league's average save percentage with the number of shots a goalie has had. The resulting number is the average goals a goalie in whatever league you're evaluating would've surrendered if they took the same number of shots as the goalie you're evaluating.
Then, this number can be evaluated against the number of goals given up by the goalie in question, finally resulting in a plus / minus number, GSAA.»