Fur is a synonym for hair, used in reference to non-human animals, usually mammals; particularly those with extensive body hair coverage.-- wikipedia In mammals, fur is evolved to keep warm, to decorate, to defense, and a lot more functions when it goes awry from its origianal purpose--of course there is no "purpose" at all. Obviously, in many circumstances fur is used for aggression, for more details and its zoopolitical implications, please see this post , which, in fact, is not sensitive but may be banned here.