8C is a cabin category. It depends on the ship as to what categories of cabins it has. You can have an 8A, and 8B, or and 8C. Even an 8D or 8M. They are all "8" so they are the same as in size or having a balcony. The letter has to do with the specific location on the ship. An 8A balcony cabin is on a lower deck, where an 8C may be on a higher deck or in a more desirable (to some) location.
Typically Carnival has category 4 cabins which are inside, category 5 and 6 which are standard outside cabins, the category 8 and 9 balcony cabins, and so forth. Suites used to be category 11 and 12 but they have gone on to different identities, such as GS (grand suite). Just go to the Carnival website and look at the ship deck plans.