We can define blogging in several ways:
First, quite simply blogging is creating a useful and informative place full of original content aimed at a certain audience set up as a web page.
Why Blog?
The reasons to blog are to increase visibility, save time and money. Blogs make money via the bloggers expertise, media exposure, and search engine ranking.
How to determine the market?
A good niche is a group of people that either have a strong passion about something or have a lot of problems.
So, there you have the simple and practical definition and reasons for blogging and now for Wikipedia's more detailed way to define blogging:
A blog (a contraction of the term "Web log") is a Web site, 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. "Blog" can also be used as a verb, meaning to maintain or add content to a blog.
Many blogs provide commentary or news on a particular subject; others 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 art (artlog), photographs (photoblog), sketches (sketchblog), videos (vlog), music (MP3 blog), audio (podcasting), which are part of a wider network of social media.
Micro-blogging is another type of blogging, one which consists of blogs with very short posts. As of December 2007, blog search engine Technorati was tracking more than 112 million blogs.[1] With the advent of video blogging, the word blog has taken on an even looser meaning — that of any bit of media wherein the subject expresses his opinion or simply talks about something.
The question most people are asking when asking to define blogging, is:
Is this a medium I can use to make money, advance my existing marketing efforts, or disseminate what one considers valuable information?
The definitive answer to this question is YES. However, like anything else one must do it right for it to accomplish the goal you have in mind.
Go here for more on the subject:
Define Blogging: How to make money blogging
Or go here for specific help in getting started:
Blogging for Cash
Blogging Advice

