The word "blog" is short for "weblog", which probably doesn't tell you much. A "weblog" is a sequential series of writings. Originally a "weblog" was meant to be a place that someone could quickly write notes, and the notes would be recorded chronologically. This makes blogging essentially a "diary". But if that's all you see a blog as being, then it's easy to dismiss them and miss the power.
Here are some of the essential features of blogging:
- Quick and easy to post new articles. The blogging system takes care of indexing the articles, and arranging them in topical and chronological order.
- Articles are arranged primarily chronologically.
- An index of articles are exported via RSS or similar syndication formats.
- When you post new articles, some blogging systems "ping" aggregator websites.
- Users can use RSS newsreaders to poll RSS news "feeds" for new content.
- There is space for the viewers of a blog to comment on the blog entries.
The RSS related features go together to act positively in drawing new readers to your site. RSS is a simple system of announcing "articles", with an author, title, some content, and the address (URL) of the full article. Several protocols have been implemented around the RSS idea, that allow specialized RSS newsreader programs to poll for new content, and allow one site to notify others that new content is available. By notifying other sites of new content, those other sites then generate links to the announcing site, and we already know that the more links a site has, the search engines will rank that site higher.
Blogs are simply a type of website. They are no different than any other website, in that they have content, and all the rules that apply to other websites also apply to blogs. If a particular blogger writes poorly optimized content, the search engines won't be able to figure out what the topic is, and be unable to send viewers to the site. On the flip side, another blogger, writing about the same topic, could do so with well optimized content, and the search engines will be able to match that site easily with people searching for that content.
Blogs are essentially vehicles for publishing writing. What an individual blogger makes of their blog is up to them. And what the world makes of them is, in my opinion, overhyped.