Page: Metrics shown in this section are derived from page level daily values.
Post: Metrics shown in this section are derived from post level lifetime values for content posted within the selected period.
Reach: The number of unique people who have seen any content associated with the Page.
Organic: The number of unique people who have visited the Page or seen any content associated with the Page in the newsfeed or ticker, excluding Sponsored Stories and Ads.
Viral: The number of unique people who have seen a Story* about their friends interacting with the Page or its content.
Paid: The number of unique people who have seen any content associated with the Page through Sponsored Stories or Ads.
Page Posts: The number of people who had any of your Page's posts enter their screen. Posts include statuses, photos, links, videos and more.
* A Story is an item that appears in a user’s newsfeed when their friend interacts with a Page or its content. E.g. “Jake commented on a post from Locowise.”
The following actions can generate stories:
liking a post
liking a comment
commenting on a post
commenting on a comment
sharing a post
answering a question/”poll”
responding to an event
claiming an offer
posting on the page wall
mentioning the page in a post
tagging the page in a photo
checking in at your place/page
sharing a check-in deal
liking a check-in deal
writing a recommendation
liking a page
For more information on Facebook metrics, please refer to the following FB developer resource: https://developers.facebook.com/docs/graph-api/reference/v20.0/insights