A pie chart is a circular chart divided into sectors the lengths of whose arcs are proportional to the percentage of the chart represented by the particular category.
A pie chart is a way to visualize:
- categories as parts of a whole.
- Only a relatively small amount of data can be fit into a pie chart.
- Arc lengths aren’t as easy to discern quantitive differences in categories as bar graphs unless there is a large difference in quantity.
- A pie chart does not show change over time.
The wikipedeia page on pie charts gives a definition and various examples of pie charts. One of which is the chart that I have attached showing the locations and relative population size of native english speakers as of 1997. Additionally, this link talks about some of the advantages and disadvantages of the pie chart. Finally, click on this link here to build your own pie chart with control over the size and number of sections.