Okay, my bad. The terminology is confusing. Let me try to explain it.
First we have four categories on this site: Climbing, Biking, Diving, and Sitting.
Within each category, we have boards. For example, in Biking Category, we have three boards: Mountain Biking, Road Riding, and Any biking.
Now, we could have child boards within each board. For example, in Mountain Biking board, we have child boards such as "Training Rides" and "Events".