The Site Usage section in the Engaged Users Overview tab, shows a breakdown of user engagement in the Fuse instance over the last 6 months. We only count users who have membership to at least one community, in order to discount users who do not yet have access to your Fuse instance. You can see the total number of users (irrespective of community membership) in the Analyser Tool using the User Accounts Created option.
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Hovering over the blue portion of the bar for May, reveals 2,754 out of a total of 3,222 users did not log in to Fuse. 
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Hovering over the grey portion of the bar for May, reveals 426 users out of a total of 3,222 users engaged with content by sharing, liking, and viewing. 
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Hovering over the pink portion of the graph reveals that 42 users out of a total of 3,222 users were active, however did not engage with any content by sharing, liking, and viewing. 
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