Rick, a blog is typically a sounding board for anyone with a voice/opinion. It typically has 1 author (or only a few). After an article is posted, readers can comment on that article, but can't start a new article or thread.

It is different from a forum as any member of a forum can be the author / starter of a topic

google now ads more SEO value to websites that correctly utilize social media. Blogs, facebook & twitter are very important for SEO.