A blog (a blend of the term web log) is a type of 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.
Most blogs (including this one) 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
Many blogs provide commentary or news on a particular subject. A typical blog combines text, images, and links to other blogs, web pates, and other media related to its topic. The ability of readers to leave comments in an interactive format is an important part of many blogs.
As of 16 February 2011, there were over 156 million public blogs in existence.
The above from Wikipedia!