A catgirl is a female with cat ears, a cat tail, or other feline characteristics on an otherwise human body. Catgirls may be found in Japanese anime and manga where they are more commonly referred to as Neko (猫) or Nekomimi (猫耳), in cosplay activities both in Japan and around the world, in video games , and in online virtual world communities such as the Nekos of Secondlife. 
Catgirls in character typically exhibit a more cat-like attitude, and may sometimes include cat gestures or sounds in written or verbal communications. A frequent running gag among catgirls is that, when talking, they habitually end their speech lines with the catchphrase nyan, the Japanese onomatopoeia for a cat's meow.
Catgirls in anime and manga will sometimes sprout cat ears or a tail in order to illustrate their excitable personalities. This is similar to the phenomenon of becoming super deformed and is mostly a stylistic quirk derived from manga. They may momentarily develop a catlike mouth to emphasize mischievous thoughts or comments by a character.
In certain anime and manga series, a boy may be compared to a cat in a similar way that catgirls are. These characters are referred to as catboys. Bishōnen catboys are typically associated with shōjo manga and yaoi; for example, Ritsuka, from the anime and Manga Loveless. Rebellious boys are more often compared to dogs or wolves. The "lone-wolf" characterization is very common for brooding, aggressive, socially isolated males, while comparisons to dogs usually refer to adorably rebellious but ultimately harmless boys.
In shōnen series, a (usually villainous) catgirl may be portrayed as the leader of a band of anthropomorphic animals.
Catgirl characters are also found outside of anime, manga, and video games. Examples include Catwoman from the Batman series (dating back to 1940), Josie and the Pussycats in the early 1970s, and characters from the Broadway musical Cats. Other less humanoid catgirls include Cheetara from ThunderCats, and the Khajiit from The Elder Scrolls series. Fantasy games catgirl characters include Magic: The Gathering's Mirri and Purraj, and the cat girl monster in the d20 Munchkin Monster Manual. Western television examples include Teenage Catgirls in Heat, and Cordwainer Smith's cat-derived Underperson C'Mell (who appears in Norstrilia and The Rediscovery of Man). The British science fiction series Doctor Who features a religious sect called the Sisters of Plenitude, who somewhat resemble Cheetara from Thundercats, but are distinctly more feline than human. See Cat People for more information. Also, Hepzibah of the Marvel Comics super-team the Starjammers, and later, the Uncanny X-Men, is a cat humanoid alien, (although she was originally more skunk-like, but that aspect has been dropped).
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- The Catgirl Research Foundation Catgirl info center - art, fiction reference, science, mythology, discussion forum, links database.
- Catgirl Community & Lifestyle Informationde:Kemonomimi#Katzen