In a chart, the Plot Area is the layer placed between the Chart Area and other chart elements such as Data Series and Gridlines. This layer typically also has the axes on its perimeter. Typically the Plot Area looks as if it is merged into the Chart Area because it is often transparent, and you can see the Chart Area through it. So, you may not be able to distinguish it from the Chart Area. This default status works well. However, you can format the Plot Area separately to highlight it. You can change its appearance by applying fills, borders, and effects with just a few clicks.
Learn about the Plot Area for charts in PowerPoint 2013 for Windows.

