It's National Blog Writing Month (NaBloWriMo). Not to be confused with NaNoWriMo, which is National Novel Writing Month.
NaBloWriMo (at least the incarnation I participate in) was started by the multi-talented (and possibly insane) Amy a.k.a. GroovyGrrl a.k.a. Soap Crone.
The idea is that you blog every day in October. Which can be a challenge. I used to blog every day (see: 757 posts in 2008), but then Facebook came along and sucked up a lot of my online posting energy.
I've been trying to post more frequently, and NaBloWriMo has prizes. Prizes! So.
You can do it, too, if you want. Click here.