NaNo is National Novel Writing Month (NaNoWriMo - shortened to NaNo) - takes place every November 1-30. The goal is to write 50k words in that time span. If you win, you become ruler of the universe...
Okay, no. I made that last part up. You don't get to rule the universe (rats)
To win, you just need to write 50k words by Nov 30th. And you get to say you won, and you get a cool little thingiemahooie that says you won (see my sig)
Anyway, many of us get into the spirit of the NaNo... and miss it when it's over