The Performance Summary widget gives you a high-level summary of the performance and content metrics for your site, and this widget is available for both real user and synthetic data. This widget contains the same information as the cards on the Real User and Synthetic Performance Detail pages.
Note the metrics are averages over the Dashboard Time Period. You can mouse over the information icon (i) for more information about each of the metrics. Also, like the Performance Detail pages, more metrics will be available for the synthetic data.
At the top, you'll get a clear view of the exact time period for the numbers, as well as the site and the selected page name(s). Configuration for this widget uses the standard set of filter options.