It's the month of November. You have 30 days to write a 50,000 word novel. Get to it!
The idea behind National Novel Writing Month is that many of us have at least one book inside of us, but we're too lazy to spend the time to write it, or simply get overcome by the scope of it all — so it ultimately never materializes. NaNoWriMo challenges that, by encouraging participants to throw caution to the wind and write without revising, without obsessing over what they're writing, but to just get the words out. (There'll be plenty of time to edit it after the month is up.)
"No Plot? No Problem!" is their slogan.
Official site, a project of The Office Of Letters And Light.
The Nano website has a list of published NaNoWriMo Novels.
Even though it is called "National" Novel Writing Month, entries are accepted from countries other than the U.S.A and in languages other than English. note It is slightly harder to complete outside North America, due to the lack of the extra hour from daylight saving time. The difference is so minimal that it doesn't really matter.
NaNoWriMo also had a sister event called Script Frenzy, with a similar goal, but executed in script format. It ran in April every year from 2007, but was ultimately discontinued in 2012.
Cosmetic Award - The first and foremost prize for completing Nanowrimo is ... the mere satisfaction of completing one's novel. And a purple wordcount meter.
Some of Nanowrimo's sponsors, on the other hand, offer slightly more tangible prizes for winning, such as CreateSpace offering to print up to five free copies of the winner's manuscript, and Scrivener offering a 50% discount off their software's purchase price.
Determinator - anyone who actually finishes a novel. Writing 1,667 words a day may not seem very hard, but doing it every day, for a whole month (especially a month with Thanksgiving and Christmas advertising) takes dedication!
Memetic Mutation: "Permissions" to reproduce a user's Nanoisms in published form quickly became "persimmons", and have since mutated into frankensteinian concoctions like "permapurplepomewhatsits".
Not Cheating Unless You Get Caught: ...actually, no one really cares if you do, either. There is even a forum just for "Nano Rebels". In a sense, NaNoers are actively encouraged to "cheat" by artificially inflating their wordcounts—No Plot? No Problem, the semi-official handbook by Chris Baty, NaNoWriMo's creator, offers several tips on how to do this.
You're supposed to start a new novel on November 1st, but some people continue working on the same novel (not a sequel) as the previous year(s).
Post Count - Some of the best-known NaNoWriMo forumgoers are the ones with the highest post counts. The NaNoWriMo forum has an entire subforum devoted to procrastination, which is filled with games and conversation threads. Some users use these threads simply to increase their post counts.
Self-Deprecation - Participants tend to frequently criticise their own novel's plot, characters, and (especially) blunders — but mostly in good humor; blunders in particular are lovingly christened "Nanoisms" (allegedly a portmanteau of "Nanowrimo" and "aneurysm").
Thread Hopping - When the quick reply method was still around, some users would just read the first post, scroll to the quick reply section of the page, and reply without reading any of the other responses, especially for threads of the "share with the group" nature.
Thread Necromancy - One famous thread on the procrastination forum is Thread Killer, in which users attempt to make the last post in the thread. Of course, the next poster unkills the thread, and users will go on for scores of posts creatively attempting to kill the thread.