It tickles me that this is on the Merriam-Webster site.

[spikesgirl58.livejournal.com]

fan fiction (noun) Definition: stories involving popular fictional characters that are written by fans and often posted on the Internet. Called also fanfic.

I have written fanfic since I was about 8 or 9. At that point, you were thought to be an odd duck or to have something wrong with you. I'm glad it's gotten to the point of where the word is at least mainstream enough for an on line dictionary.