Generally, kitsune (狐) is just the Japanese word for fox. However, when used in Japanese folklore, the kitsune is a type of youkai, and is believed to possess great intelligence, long life, and magical powers.
One of the more notable features of the kitsune are their numerous tails; they may possess as many as nine. The more tails a kitsune has, the older and more powerful he or she is, for every one hundred years they live, another tail grows. Once they have lived for eight hundred years they will have nine tails, one of them the one they were born with, and the other eight grown through the ages.
A kitsune's greatest power is that of illusion; they are able to trick a human into seeing almost anything. Because of this ability, they are regarded as playful tricksters in many stories. Some legends say that once a person has won the trust of a kitsune, it will be difficult for others to convince that kitsune otherwise.