Interpreting reach and exposure
Reach provides an understanding of the overall impact of your message or campaign. A high reach indicates that a broad base of different users found your message interesting and spread it to their followers. It often means that multiple unrelated people found out about your campaign from sources outside of Twitter. Conversely, a lower reach means that your message is likely only being shared among a smaller group of people who may be more interrelated (e.g. people in the same geographic area).
A high reach will often be combined with a high exposure. Be careful if you notice your campaign has a low reach and a high exposure, that is an indicator that you may have a core of users that are trying to spread your message by tweeting repeatedly but that your campaign is failing to take off beyond those users’ followers. A high exposure among a small group of people may mean they feel “bombarded” by your message. You may want to alter your message or seek out other ways to get more Twitter users involved to avoid over-saturating a small group.