A blog is short for weblog.  A weblog is a website that displays in chronological order the postings by one or more individuals and usually has links to comments on specific postings (according to reference.com)

To blog is the process of updating a weblog.  A blog is a weblog. 

Why do people blog?

Some people like to write and it is a means of publishing your thoughts for the world to see.  Many companies use it as a means of marketing products or services.  Others are trying to promote a cause.

The real question is "what is my goal and what type of blog could help me achieve it, if any?"

Blogging can help if your goal is to

• Be considered an expert in something
• Have your site rank high in search engine results
• Get feedback on an idea or concept
• Build an online relationship with visitors to your website