A page on the interweb, regularly updated by someone who, ostensibly, can find nothing better to do with their time.
In the past these were used as a form of diary, where the individual responsible for the blog would bitch about their daily activities. Though often incredibly banal, this could be interesting, in a voyeuristic, and rather unwholesome manner.
The recent trend, however, is for bloggers to merely reproduce news stories that they heard on the mainstream press or other blogs, and either make a brief, badly-informed comment on the story, or link to a brief, badly-informed comment on another blog. This has led to the blogosphere
increasingly resembling a gigantic, electric circle jerk
"I keep up-to-date on the news of the day by reading blogs, all of which are witty and well-informed. (I am number one jerk.)"