If you sit down and write a Nancy Drew book and publish it under the name of Carolyn Keene it's not fanfic. Right? Many people have done this.

But if you write a short story based on LotR it is. Or is it?

There are more than four hundred published Star Trek novels. (or so I've been told.) As far as I know, these aren't fanfic, are they? They're... novels.

But the novellas based on Lord of the Dance are.

Scarlett, the sequel to Gone with the Wind, is not fanfic by a long stretch of the imagination. Yet I've been told that if you write fiction using someone else's characters, it's fanfic. Period.

So what are the rules?

Okay, as I understand, Fan fiction (alternately referred to as fanfiction, fanfic, FF, or fic) is a broadly-defined term regarding stories about characters or settings written by fans of the original work, rather than by the original creator. Works of fan fiction are rarely commissioned or authorized by the original work's owner, creator, or publisher. Most fan fiction writers assume that their work is read primarily by other fans, and therefore tend to presume that their readers have knowledge of the universe (created by a professional writer) in which their works are based.

Many stories can appear to have gaps or “excesses” in the unfolding of the story: that is, they introduce potential plots which cannot be fully told or add extra details which hint at more than can be revealed. Readers, thus, have a strong incentive to continue to elaborate on these story elements, working them over through their speculations, until they take on a life of their own. Fan fiction can be seen as an expansion of these media franchises into new directions which reflect the reader's desire to "fill in the gaps" they have discovered in the material.

Hope that helped.

I think what you're running into with the Star Trek books is Expanded Universe. They have this for Star Wars too. It's a plot to make more money by telling more stories.

Fanfic is completely unofficial.

Often, it's pretty yucky too; you have to be really careful. (there are kazillions of girls who want to marry Legolas for some unknown crazy reason)

You can have a lot of fun with fanfiction; it's how I got into writing.

And then of course if you can manage to get a contract with LucasFilm to write official Star Wars fanfiction, it might even get considered 'canon'.

Why oh why do they!?

I agree that it is really fun. I don't know the rules, but it is good, enjoyable practice if nothing else.

I pretty much define a fan fiction as someone who writes their own story idea using characters they are familiar with from other books, movies, and TV shows.

I've written one fan fiction--which is not done, what a surprise --where I have used character from a manga/anime and made my own alternate ending since I wasn't happy about the real one. Shame on me for wanting a character's happiness. *shrug*

I'm actually trying to define what isn't fanfic...

If you write a full blown sequal to somebody's novel that's a story in it's own right, right? Not some spin-off. Because it's been done, hasn't it?

If you can publish it, it's considered canon, not fan fic. If it's unofficial, then it's a fan fic. (This is why, for example, SW has thousands of official novels, but LoTR has...Chris and J.R.R.)

If I go ahead and write this SW novel that I've been tinkering with, that's fanfic. But if I get permission from Lucas Arts, it's official and could be canon. I hope it will be, since it's completely original.

That would be neat! I've never looked into publishing something like that; how do you contact LucasArts (and their publisher...I forget who it is right now) to get permission?

Have you made sure it fits with all the other expanded universe books out there? (using something like wookieepedia)

You mail it to Lucas Arts, since Scholastic does not accept unsolicited manuscripts.

Oh, LucasArts does?

BTW, I'd be willing to read over it & write some notes if you get it written someday; as long as I had time, of course. (I am learning not to book myself too far into the future, lol)

Thanks, right now it's an email rpg I did with a few friends.

I guess all the Star Wars role playing games I played on the trampoline with my sister could be called fan fic. I played Luke Skywalker-as-a-child, and my sister played his best friend, a girl.

So, if an author (say, me, for example) wrote a story, but instead of building her own world, used, say, J.R.R. Tolkien's world, that would be fan fic?

Yes.

I actually have an idea for a future fanfic.

I would agree. I think the difference between fanfic and canon material is professionalism. If you get an official stamp to publish under the label (like the Star Wars and Star Trek), it's not fanfiction. Also, if you write and publish a serious "sequel" to a public domain work, it's not fanfiction. Fanfiction is unauthorized writing that's "for fun" and can't be published. Some stuff written for an existing universe, or referencing other writers' work, can be published legally with the proper permissions.

That'd be my take, anyway!

That makes sense.

Quibble: I think "professionalism" isn't quite the word you're looking for; to my mind it's more a description of quality, and while a lot of fan work is drivel at best, so is a lot of original work. (Ever hear of a "slush pile"? ) And some fan work is (except for depending on the original to make much sense) even better than the original.
And another quibble: Public domain fandoms are somewhat muddy as far as fanfic is concerned. You can legally publish what would, in any other fandom, be fanfic, but a lot of fans share it like any other fanfic instead.

I think the two main issues are authorization and motivation. If the owner of the rights to something lets you write and publish a derivative work, it's most likely not fanfic (though from my vague understanding of the Star Wars Extended Universe system, that's stil not quite clear). But if you're writing for the love of the material, and not seeking to make anything from it, and letting it freely spread far and wide, it's probably fanfic, even if the original work is in the public domain.

I agree with kingjon's categories, myself. If it's authorized, it's part of the franchise--even if it isn't canon. If it's not part of the franchise, then it's a fanfic, even if the author went out of their way to make it fit the canon as well as (or better than) some official works do.