NaBloPoMo stands for "National Blog Posting Month." The goal of NaBloPoMo is for participants to write a post a day for an entire month.
Although November was the biggest month for NaBloPoMo (with prizes and everything!) people could take up the challenge of writing a post a day during any month.
To help inspire bloggers, NaBloPoMo host sites would assign a theme for each month, and sometimes offer daily writing prompts, but both were optional. Bloggers were not required to write on a specific month's theme or a specific day's writing prompt. Any post about anything at all would count.
At the time of this writing, there is no longer an official NaBloPloMo host site, but individual bloggers sometimes attempt a month of writing on their own, or join with other bloggers and host their own mini NaBloPloMos.
