This article is from the Eddings FAQ, by Aquarius firstname.lastname@example.org with numerous contributions by others.
Fanfic (short for fan-fiction) is writings which are set in the worlds of,
using the characters of, or otherwise derived from some published work.
This includes short stories, long stories :-) and filks (songs adapted in
some way, often amusingly, to fit in with the chosen milieu).