Beginner Group: Beginners are those who are training for their first marathon or half marathon. Your primary focus is to just finish the event.  You will gradually build up your mileage during the training period. 

Intermediate Group: People who have already successfully completed at least one marathon or half marathon and usually want to improve their finishing times.

Advanced Group:
People who have run several marathons or half marathons and are trying to run faster.  These people are running over 40 miles per week already.  They will be doing speed work and races during the training period.