A popular female message board user. However, "popular female message board user" is redundant, as the lopsided male/female ratio among internet users ensures that anyone claiming to possess a vagina (even one who is secretly a man) will be held in high regard by the board's horny male users.
The forum female is a specific kind of female user, however, who deliberately flaunts the fact that she is a girl to garner attention. Her username is often something along the lines of "SexySarah5132" or "Surfer_Grrl69". Her posts are usually peppered with flowery poetry, pink text, anime smilies, and innocent sounding laughter (teehee, hehe). Often owns a blog. When the forum female is sad or angry, all she needs to do is post a whine and sit back as the horny male users all shower her with sympathy. Any attempt to flame her will be rendered useless by the legions of her forum "boyfriends", who will quickly repel any attack on her. In time a forum female may become a moderator or admin, which grants her near immunity.
Though irritating the forum female may be, there is not much which can be done, as she is more annoying than harmful.
Forum female: "hay, wut u boyz doin tonite? ;) teehee ^_^"