At my school, "full time" meant 4 or 5 courses per term. "Part time" was 3, 2 or 1.Also there were three terms per year.

So if a credit hour is an hour of class per week. Our classes all had 3 hours per week, so 4 classes is 12 credit hours and 5 classes is 15 credit hours. That fits the bill.

I think I understand now. I just hadn't been thinking of it in terms of "credit hours".