An anthro (short for anthropomorphic, meaning "human-shaped"), in the context of this site and the furry fandom in general, is a non-human animal with a human-like shape. Generally speaking, anthros stand upright and have small heads and hands relative to their body size, long limbs, and a well-developed physique. Anthros are often drawn with features usually thought of as human, such as long hair on the head, or clothing.
Anthros alone are not usually allowed on WildCritters, but, in a borderline case, if a particular post is thought to be cute enough, and the image is of a high-enough quality, we'll probably let it slip. (Just don't let it happen too often.)
As a tag, [code]anthro[/code] should be added to any post where the image prominently features an anthro character.