A publicly accessible journal maintained on the Web by an individual or group. The topics covered in a blog are dictated by the author and so vary widely: some reflect personal interests and concerns, whereas others comment on aspects of current affairs or discuss work of public interest that their author is engaged in. Some have become respected sources of information or opinion, while others are vehicles for corporations or other bodies to disseminate information and obtain feedback. Many blogs include facilities for readers to post comments and to engage in debate; in this function they have tended to replace earlier forms of online discussion, such as Usenet and forums run by online service providers. Such technologies as RSS allow registered readers of a blog to be informed of a new entry.

Blogs had antecedents before the explosive growth of the Internet from the 1990s, but, as in other areas, it was the global nature of the Web that encouraged the growth of modern blogging. It is very easy to create and maintain a blog, using freely available software and services, that can be read using a standard Web Browser; and blogs can contain links to other blogs, forming an extended online community. The term ‘blog’ was only coined in 1997, yet by the mid-2000s blogging had become a mainstream activity not confined only to Internet enthusiasts; in some professions, such as politics, it is becoming almost a required activity.