All Page admins will now be able to see impressions for each of their posts. They’ll also see the feedback rate, or what percentage of time fans “like” or interact with their posts.
Facebook is also making some changes to how monthly active users or MAUs are counted. Instead of users that actively “like” or comment on content, all unique users that see posts will get counted into a Page’s MAUs, which will drive overall numbers up.
Facebook originally introduced these feedback analytics in January to Pages with more than 10,000 fans; they help Page owners understand how much exposure their content is receiving. Impressions are how often a post is rendered in a news feed; it is not how many unique users have seen a post.