First of all you can find lots of information on wikipedia about this topic and its very accurate. defining a single person as a furry will change with each person you meet. there are different levels and scales of "Furriness" there are many different offshoots as well so ppl that that judge all furries the same are unjust.
A furry can be:
* Someone who dresses in animal costumes and sometimes attends conventions such as Anthrocon and FurMeet
* Someone who is fond of anthromorphic animals
* Someone who draws anthromorphic animals
* someone who is a furry at heart
* someone who roleplays as one, in this case their avatar is usually what they play as but they dont act as a furry in RL... and some still do too
* there are the more darker taste furries that also "yiff" whether this be with animal suits or by artwork. And if you dont know what yiff is, simply is furry porn. As i said not so nice but not all furries are even remoted interested in this.
* if you believe such thing as otherkin, some therians portray the animal spirit within them through the furry fandom.
* some furrys are furry just cos they enjoy furry cartoons or comics or even books.
Theres many different ways to be furry, some physical others not. Some distasteful and others quite accepting. I hope that helps you a bit
And for the record a furry is a humanoid animal. This differs depending on how it is displayed. Whether thru artwork, an animal mascot costume or even virtual characters online. Most furries are often more human than animal, standing upright on hind legs, many, especially in art have hands and feet instead of paws (i prefer paws still) and also many where clothes. So a humanized animal would be the best description... Mmm and not all furries are the right colors. Eg, a blue cheetah with black spots or a black horse with a rainbow mane and tail.
Furries can be any furry animal, bird and sometimes reptiles and dragons are considered furry however the common term for them now is a "Scalie". They called it furries i assume cos there are a majority of furry animals in the fandom. Birds and griffins are sometimes called avians or avian furrys.
And in the end under all this fur, we're just ordinary people that have a passion for fur and animals