A content management system is a web application to make managing the content on a site much easier than editing HTML files or working with boorish client applications. A blog is a type of website. I think the confusion might lie in distinguishing WordPress from a CMS. WordPress is a CMS, but it is specifically aimed at bloggers. Other CMSes are better equipped for handling teams, like a newsroom or a large corporate website, there there are often many teams of publishers contributing to a site.
@archaeopteryx True, Django makes life easier for web developers, but building a CMS from the ground up is really something you do if industry standard CMSes aren’t up to the task, or you’re looking for a challenging programming project. A simple CMS can be built pretty quickly in Django, but it’s still a much more complicated task than getting a site up and running in Joomla! or Drupal, even though those two CMSes in many ways function more like platforms than end-products.