A blog is a website. The difference between blog and website is simply structure and semantics.
A blog is a post based website designed for interactive communication. As the posts are frequently updated and appear on the front page of the site it’s very attractive to search engines.
What most people call a website is merely a page based site that functions as a one-way noticeboard. As the structure is page based and as pages are for static content that rarely changes, and as pages do not have RSS feeds, and as others do not backlink to pages, it is not as attractive to search engines as a post based blog structured site is.