They are differentiated from each other.
Catholicism is a denomination of Christianity; one is encompassed in the other. There are many other denominations and associations with Christianity, but they all ultimately still belong under the same title even as different as they may be from each other.
Unless, of course, it's viewed from certain religious senses, where as you could belong to any denomination but that doesn't automatically make you "Christian".
Christianity has different categories,
(Protestant)
Calvinist (also protestant)
Puritan (I think protestant?)
and Catholic (Non protestant)
And whole lot of different assorted flavors.
Some of those are denominations/movements of Christianity, and they all branch off from another in some way. Catholicism, however, is one of the oldest branches of Christianity, if I'm not mistaken. There's also Early Christianity, and Orthodox, and other such branches.
I'll take mint chocolate chip.
lol