fujoshi
Literally translated as rotten girl, it refers to a female fan of yaoi.
It should be noted that the concept of "yumejoshi" (a girl who enjoys imagining herself in a relationship with a fictional character, often through drawing and writing) has also come into use, though this is less common.
While the term otaku could be used for males and females, fujoshi specifically identifies females. Male fans of yaoi are called fudanshi instead. The equivalent words for overzealous fans of yuri are himejoshi and himedanshi.