Stateroom categories are how the cruise line designates their cabins onboard the ship. In its simplest terms they are broken up into 4:
Interior (no window)
Oceanview (with a window)
Balcony/Verandah (has a walkout private balcony)
Suite (larger square footage, more amenities)
From inside these categories there are typically additional additional stateroom categories which can offer different promotions or better locations on the ship.