You may have noticed in our Influencers tab that there is a new metric called Exposure, and this number is always equal to or larger than Impressions.
Exposure measures the total Impressions that a user has generated, including the impressions generated by their Retweeters.
For example, say @UserX has 500 followers and tweets twice. In this case, Reach = 500 and Impressions = 1,000. Now suppose that one of this user's posts was Retweeted by @UserY, who has 1M followers, so one of her posts was also seen by @UserY's followers.
Then, the total Exposure that @UserX generated was 1,001,000 (1,000 Impressions from her own followers, and 1,000,000 from @UserY's followers).
In essence, Exposure measures the total impact that a user has generated, beyond just their own followers.