Are you talking about Hunter and Hunter Seat Equitation? If that's the case, the answer to your Medal question may be different than what's given above.
"Limit" usually refers to the number of classes you can have won previously and still compete. For instance, non-Medal eq classes are rated Maiden, Novice and Limit as follows:
Maiden - juniors and amateurs who have not won one blue ribbons over fences
Novice - juniors and amateurs who have not won three blue ribbons over fences
Limit - juniors and anatuers who have not won six three blue ribbons over fences
If you're new to showing, you'll probably be showing in Maiden.