Differences between Page views, reach, and impressions
Page views are the number of times that a Page’s profile has been viewed by people including people who are logged in to Facebook and those who aren’t.
Reach is the number of people who saw any content from your Page or about your Page. This metric is estimated.
Impressions are the number of times any content from your Page or about your Page entered a person’s screen.
Bear in mind that because of the many ways content can be created and shared on Facebook, the actual number of organic impressions may not currently be reflected in this metric (or any metrics that use organic impressions, including Page views and reach).