Invented by data visualization pioneer William Playfair, Area Chart a variation of line chart by filling area between axis and line, and thus called Area Chart. Area Chart can be used to visualize multiple set of data by stacking them one by one; but there is also usages like Layered Area Chart with overlapping, translucent areas.

Sometimes area chart is filled between two lines with two different colors to determine which one is above the other. In this case we can also highlight the difference and direction between these two line; in this case, the variation is also called Difference Chart. The most famous use case of this variation is the 'Exports and Imports to and from DENMARK and NORWAY from 1700 to 1890' Difference Chart made by William Playfair.

The 'fill' property of Area Chart makes it more like a Bar Chart than a Line Chart, and thus it can be used to visualize a subtotal of values with stacked areas. On the other hand, multiple lines in a Line Chart tend to be treated independently, so it is hard for a Line Chart to achieve similar effect of a Stacked Area Chart.