Your total subscriber audience is RSS count, Twitter count, and comment feed count.
Your RSS audience includes all your email subscribers because your newsletter is powered by your RSS feed as well as anyone that just looks at your feed in a feed reader like Feedly or Bloglovin. RSS subscribers consist of anyone that is accessing http://feeds.feedblitz.com/yoursite (this includes email).
Keep in mind, email subscriber numbers are not duplicated in your Total Subscriber Audience.
When they sign up for email updates on your website, they are added to both email count and RSS count.
(back to the previous sentence)
Individual social network audiences is strictly how many followers you have on any linked social network.
See page 7 of our manual to see metrics breakdown: