A blog is a user-generated website where entries are made in journal style and displayed in a reverse chronological order.
Blogs often provide commentary or news on a particular subject, such as food, politics, or local news; some function as more personal online diaries. A typical blog combines text, images, and links to other blogs, web pages, and other media related to its topic. The ability for readers to leave comments in an interactive format is an important part of many blogs. Most blogs are primarily textual although some focus on photographs (photoblog), sketchblog, videos (vlog), or audio (podcasting), and are part of a wider network of social media.

The term "blog" is derived from "Web log." "Blog" can also be used as a verb, meaning to maintain or add content to a blog.
The modern blog evolved from the online diary, where people would keep a running account of their personal lives. Most such writers called themselves diarists, journalists, or journalers. A few called themselves escribitionists. The Open Pages webring included members of the online-journal community. Justin Hall, who began eleven years of personal blogging in 1994 while a student at Swarthmore College, is generally recognized as one of the earliest bloggers.

Blogging and the mass media

Many bloggers differentiate themselves from the mainstream media, while others are members of that media working through a different channel. Some institutions see blogging as a means of "getting around the filter" and pushing messages directly to the public. Some critics worry that bloggers respect neither copyright nor the role of the mass media in presenting society with credible news. Bloggers and other contributors to user generated content are behind TIME magazine naming the 2006 person of the year as "you".

Many mainstream journalists, meanwhile, write their own blogs -- well over 300, according to CyberJournalist.net's J-blog list. The first known use of a Weblog on a news site was in August 1998, when Jonathan Dube of The Charlotte Observer published one chronicling Hurricane Bonnie.


from : en.wikipedia.org