This is a country club goal.
Score 100 under par on Merion. This is a 70 par course
How do I score a 100 under par or does 100 under par mean something else I am not privy too?
If it’s a CC goal then it’s one that your CC has to achieve collectively not you individually although you will of course contribute. In this case it means that collectively the members of your CC have to play enough sub par rounds to aggregate -100. Best of luck.