GOR is an abbreviation for Girls on Reserve. Commonly used among adolescent boys in middle to upper class areas when describing a girl that they can get on their dick at any time. GOR is an easy and efficient way to let the other guys around you know that you have claimed this "GOR" without alerting the girl that she was actually your Girl on Reserve.
Person 1 "Zach has so much fucking GOR"
Person 2 "Yeah I know, he gets so many fucking bitches it's INSANE"