The term Kemonomimi is a popular Japanese anime, manga and game characteristic, where a person has unique looks, like animal ears or an animals tail or both on them to give a story a twist or just a bit extra.
Usually stories where Kemonomimi appears are in fantasy settings, where you can find a huge variety of them like dog, cat, rabbit and fox eared boys/girls have similar traits to their Kemonomimis, for example a character with cat ears or a tail will make cant sounds and will act like one.
The term Kemonomimi started to appear outside of Japan at the same time, when the anime and manga culture was released to the western audiences in around the 1990s.
This has prompted the world to adapt it to new content as well.
Kkemonomimi has a huge fan base because of its uniqueness all around the world and thanks to its influence, the western “cat girls” and other “animal girls” started to appear more and more in games and comics, even in animated films which didn’t come from Japan.
Because of its popularity in Japan, you can see a lots of ads with Kemonomimi girls and boys in order to boost their sales.