In Japanese, the word simply means “perverted” - although not always in the sexual sense - and does not refer to manga and anime specifically.
In English, “hentai” is the genre of hardcore anime/manga pornography. Interestingly enough, however, shoujo ai refers to something very different in the original Japanese: those fans who love Loli-style characters. Shoujo AiĪs shonen ai is the term for non-sexually explicit yaoi among Western anime fans, “shoujo ai” (literally “girls love”) is the term for non-sexually explicit yuri. Like with yaoi, yuri is often used to refer to animated/illustrated lesbian pornography though non-pornographic works are also technically yuri. “Yuri” literally means “lilly” in Japanese and is used as a metaphor for women.
The female counterpart to yaoi is “yuri” which describes any anime built around a lesbian relationship.