.
...
Report Filters, or page fields, provide filtering across the entire PivotTable.
Data fields
Data fields, or value fields, are used to summarize and aggregate data values with formulas. The values computed from the data fields make up the majority of the PivotTable.
PowerPivot
...
Data fields have different settings for how to aggregate and compute the data. The first of these is Summarize Values By, which determines the function used to aggregate the data, for example, Sum, Count, Average, Min, Max etc. The second is Show Values As, which allows you to change how the aggregation is display. For example, you can specify that you want to do a sum, but show the values as a percentage of the column total.
