Fanart (ファンアート?) is a common illustrations from Twitter, Instagram, Tumblr, Facebook, Pixiv and deviantART. A fan art is a drawing, painting, or sketch of an artist's favorite character of a television show, movie, book, and any other form of media.
It is that of illustrations Pixiv and illustrators who are member registration to deviantART is are, too. You can interested by the Post and illustrations, sometimes or dissatisfied, sometimes to delete the illustrations.
Most fan art are created by artist's who love a certain show.