A clustered bar graph is a type of bar graph in which you can display multiple qualitative data variables. Unlike a bar graph where only one bin is used per marking on the x-axis, with a clustered bar graph multiple bins are grouped together. You can see from the chart on the right that these bins are usually color coded to distinguish between each variable. The height of each bin represents the frequency being measured of that particular variable.
Clustered bar graphs are very useful when you want to compare multiple different qualitative variables. Instead of making a bar graph for each variable, you can group each variable into one graphical representation. Here gives some more reasons why you may want to choose this type of graph.
Although they call them grouped bar graphs, a short definition is given here. This site provides a guide for how to construct a clustered bar graph using in SPSS, and also sheds light on when you may want to use one.