Maybe it means someone who is "culturally" Catholic, and raised in it, but doesn't follow the religion anymore? Perhaps it's similar to a "lapsed" Catholic (You've been baptised, but you don't practice anymore- but you haven't formally renounced the faith or converted to another). I know a lot of them- it's very common in 2nd and 3rd generation children of immigrant Italian/Portuguese families. They don't go to church, and they question or are indifferent to the faith, but they don't want to tick Grandma off- who is as strict a Catholic as the come, usually.