"Capped" simply means there is a maximum scaled mark imposed on the subject. In previous years, in the scaling process of 1u religion, ppl who got 50 as their aligned mark did not necessarily get 50 as their scaled mark. It got capped at something like 47-48. So even if you got full marks in the exam, and got the maximum possible aligned HSC mark, in terms of scaling, you got a limit imposed on you.