A furry is an anthropomorphic representation of a non-human (generally speaking) creature. A well-known subtype is scalies, who are reptillian anthros. WikiFur has a well-made article on furries here and there is a list of known furries on OT here.
Many furries have shown themselves on OT throughout its history. They typically display enhanced aggression, criminality, zeal, and chaotic behaviour. The best thing to do if you find a furry is to be extra wary of them, for they are very evil and unpredictable most of the time and always looking to deceive you. The words of furries are to be taken with a grain of salt, for they rarely tell the truth, only when it is in their best interests.