Multi-set Bar Chart is a variation of a Bar Chart is used when two or more data series are plotted side-by-side and grouped together under categories, all on the same axis.
Like a Bar Chart, the length of each bar is used to show discrete, numerical comparisons amongst categories. Each data series is assigned an individual colour or a varying shade of the same colour, in order to distinguish them. Each group of bars are then spaced apart from each other.
The use of Multi-set Bar Charts is usually to compare grouped variables or categories to other groups with those same variables or category types. Multi-set Bar Charts can also be used to compare mini Histograms to each other, so each bar in the group would represent the significant intervals of a variable.
The downside of Multi-set Bar Charts is that they become harder to read the more bars you have in one group.