In pivot tables, labels from one dimension frequently are nested within another dimension. Nesting means that one set of labels is displayed as a subdivision of labels at a higher layer of data. You can change the way labels nest to emphasize different relationships.
For example, you can show Year and Quarter as data items in the Column Labels pane in the data layout. The Quarter labels (Q1, Q2, Q3, and Q4) are nested within each year label (1998, 1999). If you move Year after Quarter, each year is displayed as a subset of each quarter. Q1 values are broken down by labels 1998, and 1999.