A blog (weblog) is basically a regularly updated webpage that
has links to other websites with relevance to a certain subject.

For a definition - look at http://en.wikipedia.org/wiki/Weblog

They have all the attributes necessary to really boost Your Website Rankings...
1) They are updated regularly-meaning Search Engines index them regularly
2) They are keyword rich
3) They attract repeat visitors. These repeat visitors are very highly targetted!
4) They develop loyalty over time
5) Other websites can link to your blog s articles - win win win!
6) Providing fresh content elevates your status to expert
7) Very easy to update

-
1. Blog  < a blog They’re quick and easy to update, can be informal if appropriate and can develop a large user base.  They can be used to help 2 way communication and be informative
2. Customer Reviews -  allowing your customers to review you,your products and your service can open a valuable communications channel.  It can also increase customer loyalty.
3. Regularly updated content - One key factor in SEO is frequent updates to your site’s content – search engines will love you for it and this will certainly help your overall SEO strategy and natural listings. Of course, content has to be relevant, but in turn this will build your presence as an authoritative figure in your field