|Any excuse for a Zena pic|
The WIKI defines fan fiction thus: Fan fiction (alternately referred to as fanfiction, fanfic, FF, fanon, or fic) is a broadly-defined term for stories about characters or settings written by fans of the original work, rather than by the original creator. Works of fan fiction are rarely commissioned or authorized by the original work's owner, creator, or publisher; also, they are almost never professionally published. Fan fiction, therefore, is defined by being both related to its subject's fictional universe while simultaneously existing outside that universe. Most fan fiction writers assume that other fans are reading their work, so their readers have knowledge of the canon universe (created by a professional writer) in which their works are based.*
The deeper you look the more you find out that amongst the mostly forgettable stories are a not inconsiderable amount of gems - well written, imaginative use of well known characters.