A blog is a discussion or informational website published on the World Wide Web.

A blog (weblog), consists of discrete, often informal diary-style text entries (“posts”). Posts are typically displayed in reverse chronological order, so that the most recent post appears first, at the top of the web page.

Until 2009, blogs were usually the work of a single individual or a small group, and often covered a single subject. In the 2010s, “multi-author blogs” (MABs) have developed with posts written by many authors. MABs from newspapers, other media outlets, universities, think tanks, advocacy groups, and similar institutions account for an increasing quantity of blog traffic. The rise of Twitter and other “microblogging” systems helps integrate MABs and single-author blogs into the news media.

The emergence of blogs in the late 1990s coincided with the advent of publishing tools which facilitate posting of content by non-HTML users. Previously, a knowledge of HTML and File Transfer Protocol had been required to publish content. As such, early Web users tended to be hackers and computer enthusiasts. In the 2010s, the majority are interactive Web 2.0 websites, allowing visitors to leave online comments. It is this interactivity that distinguishes them from other static websites.

In that sense, blogging can be seen as a form of social networking service. Bloggers do not only produce content to post on their blogs, but also build social relations with their readers and other bloggers.