Community owners or managers need the ability to monitor the adoption and participation in their community. The Community Metrics component lets owners see metrics based on users, participation within the community, and content in the community. Additionally there are metrics for each application within a community under ‘All Metrics.
Here's a quick 3 minute demo that I created so you can see how it works.
Equivalent functionality is available for the org admins to see metrics at the global level across all communities deployed in the system.