A blog carnival is a summary of recent posts on an interesting topic. A typical carnival appears weekly or monthly, and moves from blog to blog with each edition.

If you're into math, go check out the first Carnival of Mathematics. There's something for everyone:

I’ve gotten plenty of submissions that span the entire gamut of math-blogging: education, pure math, applied math, debunking bad math - it’s all there. Only the gender distribution could be made slightly more equal (and that’s an understatement). I’m linking to the posters in roughly increasing order of mathematical difficulty, but don’t let my opinions deter you from reading the posts closer to the bottom.

Why study math? Even the most abstract math has an uncanny tendency to solve unexpected problems:

[T]he enormous usefulness of mathematics in the natural sciences is something bordering on the mysterious and [there] is no rational explanation for it.

And since I've started hacking on Haskell, I've been equally surprised at how often deep math can solve real-world programming problems.