Literally "nine tails", refers to foxes (or fox-eared characters) with nine tails. This is stated in Japanese lore to be the pinnacle of age and power for a kitsune, and takes at least 800 years to attain, 100 years for each extra tail the kitsune grows as their power and age increases. Kyuubi are supposedly near-godlike in power.
Characters named Kyuubi:
Notable Kyuubi characters: