Here's how the website describes the Retweetability Index:
The ReTweetability Index measures and ranks Twitter users based on the infectious power of their tweets. This number accounts for number of followers and Tweets overall, so it is a true indicator of infectiousness.
There is some math involved, but in simple terms, users with a high ReTweetability Index have a greater percentage of their content spread by a greater percentage of their followers, implying that when they do tweet, it's worth reading.
For those who are saying "Tweet? Twitter? Have you lost your mind?" Twitter is a service for friends, family, and co–workers to communicate and stay connected through very short messages. It's kind of like a cross between a blog and a chat room. KaBOOM! has been using Twitter for over a year. You can follow us here.