A weblog

A weblog, or simply a blog, is a web application which contains periodic, reverse chronologically ordered posts on a common webpage. Such a Web site would typically be accessible to any Internet user. The term "blog" came into common use as a way of avoiding confusion with the term server log.
Blogs run from individual diaries to arms of political campaigns, media programs and corporations, and from one occasional author to having large communities of writers. Some are maintained by single authors, while others have multiple authors. Many weblogs allow visitors to leave public comments, which can lead to a community of readers centered around the blog; others are non-interactive. The totality of weblogs or blog-related webs is usually called the blogosphere.
The format of weblogs varies, from simple bullet lists of hyperlinks, to article summaries with user-provided comments and ratings. Individual weblog entries are almost always date and time-stamped, with the newest post at the top of the page. Because links are so important to weblogs, most blogs have a way of archiving older entries and generating a static address for individual entries; this static link is referred to as a permalink. The latest headlines, with hyperlinks and summaries, are offered in weblogs in the RSS XML-format, to be read with a RSS feedreader.