If you have read the little essay about comics no longer being comics but sequencial art or manga, or if you already are a manga otaku, you will know, why the new vocabulary concearning manga contains so much Japanese.
As I said: "neko" is japanese and means "cat". Nekomimi is the term for "cat girl" (well, "cat ears", really - see below), but you might aswell only use the short "neko", even if you mean "nekomimi".
Artists and writers have been mixing animals and humans for ages - literally :)
The Ancient Egyptians had a whole pantheon of gods, being half man - half animal. The Ancient Greek mythology is full of mixed creatures, the Sphynx being the most famous.
Until today humans with animal attributes or animals with human attributes are influencing our culture and everyday life.
Manga is no exception. Those "crossbreeds" are usually generaliesed as "anthro" - from "anthropology", the science of human beings.
If an anthro is more animal then human, you refer to it as "furry". Furries usually have fur (surprise surprise) and an animal head, but they can talk and move on two legs. Your typical Disney-Duckburg-mammal-citizen would be a furry. You might also non-fur-wearing anthros "furry"; it is a generally accepted term.
If an anthro is more human then animal, you refer to it as "kemonomimi", which means "animal ears" in translation from japanese. But some people do not make that difference, calling anthros furries and vice versa.
As "neko" means cat, "nekomimi" means "cat ears" and it is not gender-specific. But as cat girls are much more popular than cat boys, your encountered nekomimi will be mostly female.
Anthros, kemonomimi or nekomimi in particular are often subject to erotic fantasies, combining female human sex with cuteness and cuddlyness. This has nothing to do with zoophilia/bestiality (sex with animals). Please approach the topic more from a shamanistic side - American Indians attach an animal soul to every human for example and Europe´s history is full of men with animal attributes expressing parts of their personality: Holy John The Eagle, Brunswick´s Henry The Lion - or today: Tom "Tiger" Jones or Eldrick Tont "Tiger" Woods.
Anthros are exactly the same - and of course you would see the personality behind the exterior - apart from the Playboy Bunnies, perhaps ^^
If someone calls himself or herself a furry, the person is not running around in some animal costume but referring to a certain animal-soul living inside - although... I DO know furries actually running around in a fur costume all day, but they are more an exception :D
Now you know what a neko or nekomimi is. They are extremely popular, especially in Japan and there are quite a lot of famous nekos who are appearing in countless manga, anime and videogames.
Acceptance is growing, minds are opening: you can buy mind controlled robot-cat ears and -tails that express your feelings and you can have sex with alien Turians, Quarians and Asari in EA´s video-game success "Mass Effect".
This site is dedicated to Kyoko Torasama, a neko from outer space, marooned on earth, trying to understand the human nature and trying to get laid. Aren´t we all somehow?
Here are some thoughts about comics in general