The community that surrounds a tv show/movie/book etc. Fanfiction writers, artists, poets, and cosplayers are all members of that fandom. Fandoms often consist of message boards, livejournal communities, and people.

Fan Domain
A domain in the internet about a comic, a book, a tv show, a video game etc. There are several fandoms all around the internet, where fans converge and the comunities are really big, many have forums, fanfics, fanart, etc.

The microcosm made up of people who are fans of a fiction genre, or of a subgenre, who have their own clubs, conventions and amateur magazines (fanzines), dating back (in some cases) to the early 1930s. Some of these are overlapping. Star Trek fandom, for example, started in science fiction fandom and eventually became a separate fandom on its own. Comics fandom and even rock (music) fandom also started there before becoming separate entities.

A kingdom of fans

In fanfiction; the movie, TV show, book or other medium that a fanfiction is written about.

1. The most disturbing phenomenon of our generation.

2. A group of people all obsessed with the same thing. Usually a work of fiction being either a movie, book, TV show, anime, comic, video game, etc...

3. A way for lonely people to feel a part of something larger than themselves.

4. A collective of creepy obsessive type people that only serves to feed and encourages each other in unhealthy obsessions and exaggerated exultation of non-existent people, creatures, places and objects.

In terms of any literary/visual media, be it TV show, movie, book, play, cartoon, or comic book. The characters, plots, and settings therein.