While there has been considerable variation on the kitsume theme, especially in 'furry' circles, the basic definition is a alopecoidal or alopecomorphic [foxlike or shaped like a fox] anthropomorphic form especially one that is capable of taking the form of another creature. Although now there is no strict limit on tails, nine has for a long time been the traditional maximum.
Kitsume in legend were 'fox madiens' some evil some good who could transform from human into fox form. One of the most evil is said to have married an emporer and made his former wives 'dance' in a pit filled with snakes and hornets. [In the end she was turned into a rock, guess thats the way the granite crumbles.]
Edit: FreeLance, I just saw one heck of an (angry) fox heading your way...
Derby: Content replacement. A filtered word was replaced.