A blog is a mix of personal and project writing that comes from a participant or contributor.

The idea of a blog planet is to show the width and depth of personalities in a community, and what they are doing.

It intentionally allows for personal expression. In other words, the content is not all community specific. It is sometimes wildly off topic.

The Fedora Planet is a good example, with blogs aggregated from willing contributors. People add themselves to the planet, and it is a mix of languages, topics, skill levels, and project interest. All aspects of the Fedora Project are covered there on a daily basis, with a wide variety of contributors from Packaging, Art and Design, Marketing, upstream development, and so on.