Reports can be accessed as "Channels" or Cross-Channel". Channels allows you to view information from a specific network, and Cross-Channel shows comparative information across all your network accounts. This section allows you to view analytics online or export custom reports.
Engagement - the amount of interaction (likes, shares, comments) a piece of content receives.
Impression - The number of people who viewed your piece of content
Organic Reach - The number of unique people who saw your content in the News Feed, Ticker, or on your page for the selected time frame without paid promotion. This includes people who have liked your page, and people who haven't.
Average Engagement Rate - Individual post engagement compared to overall followers.
Facebook Specific Definitions
Page Mentions - The number of times users tag your page in posts allowing their friends to link directly to your page from the post or comment.
Total Reach - The number of unique people who have seen any content associated with your Page during a specified time period. This includes people who view your Page posts, people who visit your Page after searching for it, and people who see ads that are associated with your Page.
Post Reach - The number of unique people who have seen a particular Facebook Page post in their News Feed.
Twitter Specific Definitions
Mentions - Mentions are defined by the @handle being in the body of a user tweet, but not necessarily at the beginning of the tweet.
Retweets - A retweet is when a user shares a post of another user with their followers. Twitter enables this action with their "retweet" button.
Potential Impressions - The total number of times a tweet from your account or a tweet mentioning your account will appear in someone's Twitter feed during the report period (does not imply that a user viewed his or her Twitter feed during that time).
Potential Reach - The sum of all the followers of all "Unique People."
Engagement per Tweet - The total number of replies and retweets to one of your tweets.