It is difficult to describe what blogs are. I can describe how blogs generally look like: it looks like personal journal with a monthly calendar for navigation. I can talk about how blogs are linked together for communities. I can also talk about how ease of use and interactions with other bloggers make blogging an enjoyable and rewarding habit. Still, most people don't understand how blogs differs from other websites.
Here is another effort to find the true nature of blogging. First, I started with people's tendency to associate blogs with news. News is, literally speaking, anything new. People are attracted to all kinds of news. Once we have news, we feel compelled to share it with others we meet. Attraction to news and compulsion to disseminate news are so strong that I suspect that they are survival instincts common to pack animals.
Based on above line of thinking,
A blog is both a source of and a mean for dissemination of news. A blogger is a pack animal foraging for and sharing news via his/her blog. A blog community is a pack of bloggers who regularly share news.
This is not complete since same set of description can be applied to mailing lists and Wikis. The missing ingredient that blogs have and others don't is this: promise of more. Like your local baker, each blogger implicitly makes a promise to write more soon. This promise of more is what draws others to the blogs like the way Cheese does in Who Moved My Cheese?
Hmm. I am not sure if I got anywhere. I am more likely to start a religion than find a simpler description of blogs if I continue this line of thinking.
Update: The head mongoose, standing at top of the mound, screamed "A bomb exploded Wednesday in a mail room at the Yale University law school." Now pass it on, my fellow mongooses.