Hentai is an abbreviation of hentai seiyoku, a Japanese term for an abnormal sexual desire or act. Hentai works are often self-published and form a significant portion of the market for doujin works, including doujinshi.
See also: Nutaku, Ahegao, Ecchi, Hentai (disambiguation), Tentacle erotica, Cry (Cigarettes After Sex album).