This category pertains to how totals are displayed in the Summary bar at the bottom of each Sub-Grid.
Total Column Name
This Sub-Grid property designates an alternate Column name to be displayed in the Sub-Grid summary totals. This must be either a Number or Currency Column type.
This is a great feature when you have more than one item in a Sub-Grid such as multiple Opportunities. In the example below, the totals are displayed using the “Revenue Potential” field: