bubble chart
A bubble chart displays three dimensions of data in a two-dimensional format. With a bubble chart, all three dimensions are numeric, as opposed to column or line charts, where one axis is numeric and the other is a category.
The horizontal and vertical axes represent two of the three dimensions, as in other charts. The size of the colored circle, or bubble, for each data point represents the third dimension.
You can specify the chart type and subtype for a report definition report by using the Chart Editor.