Nested bar charts are multi-series charts, with the vertical bars displayed one within another, creating a visual effect of containment. It's like each series' bars are contained within the bars of the background series.
Our Global Sales demo charts show groups of product quantity totals sold in US, France and UK, in three different years. The multiple series are the US, France and UK countries. The values for each year are 2007, 2008 and 2009. Remark the vertical X axis is a category axis: year values are distributed at equal intervals on the axis. Quantity value bars for each year are displayed one within the other for each country, with a containment visual effect. It's like each bar contains another. All bars for a specific country have a different distinct color. First country uses the first palette color, second country the second palette color and so on.