The number of times that a post from your Page is displayed, by organic rather than paid sources.
Why It's Important
Improving organic impressions means making it into News Feeds more frequently and optimizing your marketing tactics for Facebook’s EdgeRank algorithm.
How to Use It
To improve organic impressions of your content, you should focus on growing the number of active and engaged fans on your Page, placing emphasis on shareable content, and limiting the negative feedback you receive.
By looking at impressions, reach, and engagement levels side-by-side and with differentiation between organic and paid efforts, you will be able to tell how well you are succeeding in these endeavors, and how these metrics relate to one another.