Fanfic or fanfiction is broadly-defined fan labor term for stories about characters or settings written by fans of the original work, rather than by the original creator. (Source: here)
I have read a fanfic, the only one i think:p Its a fanfic of Harry Potter. I got it from a friend, and curious about what fanfic was all about. IMHO, the one i read was not good at all. Its faaaaar away from the original author, JK Rowlings.
I never read any fanfic until now:)