Put loosely, if it has to do with animals that look like humans or at least behave like humans, it's furry. As you can imagine, this is a fairly loose definition, and spans everything from Bugs Bunny cartoons to popular movies like Disney's The Lion King.

Unlike most other fandoms, which are often centered around a corporate creative property (such as Star Wars or Lord of the Rings), Furries have a looser fandom affiliation and are basically "fans of each other" as opposed to being fans of a high-profile television show. Sometimes furries will attempt to create characters based off of preexisting worlds (Sonic the Hedgehog, for example, has spawned off many fan-characters), but most don't.

As a result, many fans within the fandom will often create personal characters as a means of expression/'branding' within the fandom, and there are a significantly higher portion of fans who are also artists for hire or otherwise attempting to start businesses within the fandom. As a result, there are large amounts of art that exist within the fandom, and even more people willing to pay for it.

What the 'art' in question is can vary as much as the fan(s) involved in making it. Most will stick to drawings and illustrations of furry art, while others will create plushies or "pawpets" (furry puppets - think Kermit the Frog), or full-body costumes known as "fursuits" for the purposes of representing their characters at conventions, much the same way someone might "cosplay" as their favorite anime or video game character at other conventions.

In short, the fandom is whatever you need it to be -- so have fun with it!