Pie and doughnut charts are used to display numerical proportion between data as parts of a whole. Each data value is represented as a slice, which represents a proportional quantity. These charts are very popular but are also widely criticized. Since we don't perceive angles very well, it's much harder to compare data displayed in a pie chart, than in a bar or line chart. Using pie charts to compare only very small sets of data can avoid or reduce these problems.
A pie chart is usually used to display a single dataset. The type property of the chart object should be pie. Doughnut charts are equivalent to pie charts, but they are created with type: doughnut. You can also transform any pie chart into a doughnut by simply changing the dataset property cutoutPercentage to 50 (or some other value different than zero).
