Aggregation functions by default aggregate over the current selection of field values. The current selection can be referred to as a set of field values. You can define other sets of field values and use them in your charts instead of
the current selection. For example, in a dashboard you may want to show market share a product across all regions irrespective of the current selections. Defining a set of field values is referred to as defining a set expression
and using set expressions to analyze data is referred to as set analysis.
