I have no idea what the Blog is until I found this on http://en.wikipedia.org/wiki/Blog
A blog (a blend of the term “web log“) is a type of website or part of a website. Blogs are usually maintained by an individual with regular entries of commentary, descriptions of events, or other material such as graphics or video. Entries are commonly displayed in reverse-chronological order. “Blog” can also be used as a verb, meaning to maintain or add content to a blog.Most blogs are interactive, allowing visitors to leave comments and even message each other via widgets on the blogs and it is this interactivity that distinguishes them from other static websites. 
Now I know it is another way of communication after Email、BBS and IM. People can easily post their diaries, thinking, status and even photos, videos on their blog, this is a more effective way to communicate with your friends and family even people that you do not know. You can customerize your blog’s home page, design your layout and even plug in background music.
Here is the history of the blog.
The term “weblog” was coined by Jorn Barger on 17 December 1997. The short form, “blog,” was coined by Peter Merholz, who jokingly broke the word weblog into the phrase we blog in the sidebar of his blog Peterme.com in April or May 1999. Shortly thereafter, Evan Williams at Pyra Labs used “blog” as both a noun and verb (”to blog,” meaning “to edit one’s weblog or to post to one’s weblog”) and devised the term “blogger” in connection with Pyra Labs’ Blogger product, leading to the popularization of the terms.
I am not interested in the blog’s history at all, I am only interested in the function and the way it communicate with my firends. I think it is really cool and a technic that I would love to use in the future.