by the by, can you give me a simple definition of "fan fiction"?
Have often wondered - i know the shades of grey thing was supposed to have started off as that.
Hopefully you won't tell me to just google
Basically, you're playing in someone else's sandbox, when really, you shouldn't be.
Fanfic sits in a grey area in terms of copyright, so it can be frowned upon, and, if using more than a few lines of original text, can also be seen as plagiarism. Which is why most if not all pieces published online will have a disclaimer saying that XYZ belongs to author ABC and you're only borrowing the characters for a little while.
Because of that, fan fiction is strictly not-for-profit, which makes me wonder how 50 Shades got past the safety net.
Some authors and film / TV franchises actively encourage fan fiction (Star Trek in particular, who then ran a competition to get new authors in, and published the best stories in a series of books), whereas others will issue cease & desist orders regardless of how good the quality of the writing is.
I try to avoid most of the common pitfalls in my own fanfics (set in the Babylon 5 universe) by using mainly original characters and writing about events that lie parallel to the main story arc - alluded to in the series, but never touched.
There used to be a fan fiction dictionary on jumpnow.de which was incredibly useful, but the website has been defunct for a fey years now. It might still be available on some archive online somewhere