Original: Before 1981, it was awarded to the goaltender(s) of the team allowing the fewest number of goals during the regular season; now, the William M. Jennings Trophy is awarded under the aforementioned definition.
Simplified: Before 1981, it was awarded to the goaltender(s) of the team allowing the fewest number of goals during the regular season; now, the William M. Jennings Trophy is awarded under this previous definition.