If my Latin serves me correctly, the phrase means something like “hatred of the faith.” I don’t recall ever seeing this phrase in any Catholic documents or teaching, though (whether to refer to protestants or to anyone else). Where did you encounter this phrase?
I suppose it could refer to the original people who invented protestantism (Luther, Calvin, etc), and to some modern anti-Catholics. But I think most protestants today don’t give Catholicism much thought at all.