Oh boy. Shall I add my 5 cents to the already giant pile? I feel like “what is a fluffy?” is pretty much the fandom’s version of philosophy’s “what is human?” When I was researching KMEB, I came across comments that claimed that what KMEB drew wasn’t fluffies. That is most definitely spite, but the fact that there are disagreements on what fluffies are still stands.
Now, my perspective. First of all, “a fluffy” is a concept that commonly consists of these components:
1, it’s an unnatural, artificial creature
2, it obviously has noticeable amounts of fluff
3, its fluff has a large range of possible colors; rarely, it can also have simple patterns
4, it has stunted intelligence around the level of a human child
5, it talks in fluffspeak
6, its physical capabilities are very limited
7, it is capable of breeding very quickly
8, it normally gravitates towards humans and seeks their attention and love
9, it matures quickly and doesn’t have a very long life span
Those are the basic ideas. Some of them are not set in stone and instead depend on a creative’s vision. Therefore, aberrations that come outside of the common framework may naturally appear, but are not looked upon favourably when overdone. Some ideas may be added up to the already existing, sometimes even replacing one or two. In that case, the rest need to be clearly present to signify that it is, indeed, a fluffy. Certain boxes allow for more experimentation, specifically, weirdbox and horrorbox.
As for anthros, I don’t feel that it is that complicated. The most important difference is that they are upright and have more prominent human-like features. But those features can’t completely overshadow thoes of a fluffy, because anthros as a concept are derived from fluffies. A question may arise, how do you compare anthros to fluffies if their features are also unclear? It’s simple: compare the artist’s basic anthro to their basic fluffy. If their fluffy doesn’t clearly go way beyond the basic concept and the anthro is clearly derived from that fluffy, then it’s definitely an anthro fluffy and not furry. By “derived” I mean that, despite the addition of more human features, a lot of intrinsic fluffy traits are still present.
That’s it for me, hope this perspective is useful.