To view the list of Summary Reports, click on Reporting from the left menu > Summary Reports. These are pre-defined system reports based on the features enabled within your site.
The Summary Reports list appears like this:

Here is some example output from the Issues by Priority report:

Export Summary Reports
If you wish, you can export any Summary Report after running it: Simply click on either "Export to Excel" or "Export to CSV" while you are viewing the report results.