I know, scielle, this doesn't make any sense at all! Its one of those things that's hard to understand unless you've tried it, and even then it can be a mystery.
Microblogging (or even "lazy blogging) is a pretty good description. If you follow a number of conventional blogs, and check them regularly, its kind of like checking tweets. However, the tweets are strictly limited in length, and get pushed to you in a steady stream. Because they are so short, they can come pretty fast, and some of them even begin to resemble haiku. The only tweets you see are those from people you voluntarily choose to follow. You can also search tweets, and there are other ways to filter the stream you see.
I understand that there may be some demographic issues at work here. Twitter tends to have a slight older population than some other social media activities.
Maybe I should leave it to Ev Williams, Twitter co-founder, to try to explain it. Here's his talk at last month's TED conference:
http://laughingsquid.com/evan-williams- ... -ted-2009/