Facebook – and the EdgeRank algorithm
EdgeRank was introduced in 2013 to prioritise posts and provide Facebookers with more accurate information for an overall better user experience.
When you have a Facebook page, each time you write a post it will potentially appear on your followers' walls. How often your post appears is based on an algorithm Facebook calls "EdgeRank". EdgeRank uses three factors - age of the post, affinity with the specific user and weight of the post. "Facebook reach" describes the number of people who actually see one of your posts.