A catagory is a group of cabins in a certain section of the ship, you should be able to look at the cruiseline brochure and find the catagory and floor your cabin is on. Usually, the higher up you go on the ship, the more money it costs. Some people prefer mid-ship because you feel a little less ship motion. Before you book any cabin or catagory guarantee, be sure to check it out on the ship layout and see if thats where you want to be. For example, how far away from elevators, if you use them instead of stairs, how far is the dinning room? All, you need to decide before you book any cabin.
Good luck and enjoy!