A website that aspiring writers can use to express their ideas of what can happen in TV shows, movies, books, plays, etc. Unfortunately, about 95% of the website's content is teenage hormone driven porn.
Don't me wrong, I read/write for Fanfiction.net quite often, and if you're patient, you WILL find something good and worth reading. You'll just have to dig through a lot of garbage first.
Fanfiction.net also has a sibling website, Fiction Press, which is for original content.
Often abbreviated as 'Fanfiction' or 'Fanfic'
"You should check out my new story on Fanfiction.net!"
"Check this out! After an hour of browsing on Fanfic, I found a story that's actually really good!"