Sunburst is like a stacked pie chart. It is also based on the same Hierarchical concept like Circle Pack
If you hover on any part, it gives you the total numbers for that slice. If you hover on the center it gives the grand total.
If we click on any section and if it has other leaf nodes then it will drill down and show corresponding sunburst for that segment
In the above figure, we clicked on the "Paper stuff" and it is showing only the categories for that product line.