Read this on BBC News.  Merriam-Webster defines blog:  "BLOG noun [short for Weblog] (1999) : a Web site that contains an online personal journal with reflections, comments, and often hyperlinks provided by the writer".

MW says that the term "blog" was looked up more than any other word this year.  Wow!  I'm not really surprised since this is the year I started blogging.  I really started blogging just to mess around with the .Text application but I guess I'm now a blogger, for now anyway.  :-)