Reposted from here.
National Novel Writing Month is a fun, seat-of-your-pants approach to novel writing. Participants begin writing on November 1. The goal is to write a 50,000 word, (approximately 175 page) novel by 11:59:59, November 30.
Valuing enthusiasm and perseverance over painstaking craft, NaNoWriMo is a novel-writing program for everyone who has thought fleetingly about writing a novel but has been scared away by the time and effort involved.
Because of the limited writing window, the ONLY thing that matters in NaNoWriMo is output. It's all about quantity, not quality. The kamikaze approach forces you to lower your expectations, take risks, and write on the fly.