Roman Catholicism
Formal or historical term for Roman Catholicism, often used in contrast with Protestantism or in older texts. In modern everyday language, カトリック is more common.
I learned about the differences between Catholicism and Protestantism.
Catholic catechism
公 (public, official) + 教 (teaching, religion). A Sino-Japanese term historically used to refer to the 'public teaching' of the Roman Catholic Church, as opposed to other Christian denominations.