One or more cross product groups:

In the layout, a Cross Product Group   is represented through the intersection of the across and down dimension groups.  Therefore the cross product group displays all possible combinations of the values of the across and down dimension groups.

When the report is run, it expands, and every example of data intersection becomes a separate cell.

One cell or filler groups

The Cell Group holds data which is used to fill the cells created through the cross product group. Whenever the report is run, these values appear in the appropriate cells.