Traditionally, the propeller and rudder were different systems, serving two different functions, propulsion and steering. Most if not all of the Fantasy Class ships use a diesel electric version of that system along with independently steerable rudders.
Azipod (Azimuthal Pod) is basically an application of an outboard motor concept. The entire prop motor pod rotates on a vertical axis (Azimuth) for directional control. Even prop rotation can be manipulated in the horizontal plane for pitch control, and the attack angle of the blades can be adjusted to enable direction change without stopping rotation altogether. What further sets it apart from the outboard concept, besides the pod being completely under water, is that the propellers are mounted on the front of the pod. Instead of pushing the ship through the water, they pull the ship. A similar, single motor scheme is marketed for smaller vessels under the name Z-drive. There is even a scheme used on some larger ships where azipods face fixed propellers mounted in skegs to achieve greater cavitation management, thus greater fuel efficiency. One of the large RCCL ships (Adventurer?) uses a 3 prop system. Azipods are mounted port and starboard, but a fixed traditional propeller is mounted on the keel's center line. The larger, newer Carnival ships probably use a similar scheme.
I may dwell on the land, but I live at sea!
Sensation 2/03 I disembarked, but never really left the ship.
Enchantment 9/03 Just had to go back.
Inspiration 3/04 Just have to go back again, and again, and again...
Sensation 04/05 The vessel made me do it!
Summit 03/06 It's Margaret's fault!