The Heatmap shows the Engagement Minutes of the people in your Account List, grouped by Role and Department, over the past 3 months.
Using the custom option, you can change row and column headers to get better data.
Pro Tip: Change the rows to Program Name or Details to see which activities certain roles engage with most.
Want your admin to customize the rows and columns? Tell them to look here.
Want this natively in Salesforce on the account page? Tell your SFDC admin to read this.