One of the many, many subcultures that can be found on the internet. As far as I can tell they like to draw anthropomorphic animal porn (mostly furry animals) and 'Yiffing'.

Quite what 'Yiffing' is, is a mystery to me and I would prefer to keep it that way.

EDIT: Rye beat me to it. That'll teach me not to spend time looking up the correct spelling for anthropomorphic.