I confess to puzzling a bit over this term when I heard it recently. Here’s a clear explanation in a recent article about BlogOn: “technology that enables online interactive exchange among users.” By that definition, blogs or Weblogs are a subset of social media. Trackbacks (or comments) are the “interactive” part of blogging. I.e. when blogs refer to other blogs. Wikis (a kind of group blog) are another subset. Read the full article about BlogOn: Is Social Media the Next Online Wave?