What is meant by post “reach” and “engagement”?

When you see the word ‘reach’, it refers to how many have seen your page or post. It is a mixture of:

• Organic reach: the number of unique people, whether they are fans or non-fans, who saw content about your Page in their News Feed, Ticker or on your Page.
• Paid reach is the number of unique people who saw an ad or Sponsored Story that pointed to your Page.
• Viral reach: is the number of unique people who saw this post from a story published by a friend.

When you see ‘engagement’, it refers to the percentage of people who saw your post that liked, shared, clicked, or commented on it.