There's really is no definitive answer. It's an animal with human characteristics. As far as what animal, and how much of a blend it is, is something nobody can agree on. There is no organization that we all belong to, so everyone enjoys this stuff in their own way. Just good clean furry fun for all ages.
All files uploaded have to pass a set of rules.
It's divided up by artist, which is the only real way to organize it. Then indexes based on other data, such as date uploaded can be made after the fact. This is the coolest part of the whole site I think. You can see a little image of each picture before you download the whole thing. Up to date.