Furries are a community off-shoot of the broader sci-fi fandom that started in the 1970’s, characterized by a fondness for anthropomorphic reprisentation in media. It expanded from it’s sci fi roots into fantasy, alt-historical fiction, slice of life, and yes, porn, because nerds are horny.
Furries is also the term for the characters that are created by the members of the community, and also has been used to describe other characters in other media, but it’s worth noting that not all of these come from furries (the people), though by now nearly all do. The lead character artists for Zootopia and Sing are out furries, for example. And Vivziepop and the Lackadaisy team certainly are furries.