The community of blogs and everything else related to them.
The blogosphere arose from the idea that all blogs exists as a heavily inter-connected community, so much so that it has become like a social network in itself. The blogosphere consists of everything that has to do with blogs: posts, comments, and its users. The blogosphere is given importance for its potential for indicating public behavior and sentiment. Marketing agencies, media groups, and even government bodies now try and tap into the blogosphere when performing company research.
see also: Blogging Tools
An empire gives way (Blogs are growing a lot more slowly. But specialists still thrive.)
The Economist (June 24, 2010)