Fanfiction, "fan fiction", or "fanfic" is produced by individuals who use the world, characters, or other elements of a preexisting creative work (book, TV show, movie...) to write their own stories.
"A transformative work takes something extant and turns it into something with a new purpose, sensibility, or mode of expression.... Transformative works include but are not limited to fanfiction, real person fiction, fan vids, and fan art.
"The Organization for Transformative Works (OTW) is a nonprofit organization run by and for fans to provide access to and preserve the history of fanworks and fan cultures." http://transformativeworks.org/
The Prezi from ILF2013 can be found here.