Hi Amarilis.

We call them that because most pies that you bake (at least where I come from) are made in round pans. So the shape is circular. In addition, when you consider a section of a circle graph, it is in the shape of a slice of the pie, because we usually cut a pie as a circular sector:

Sometimes people think it is a "pie" graph because the word sounds like the greek letter π which is used a lot in circle calculations as well (I'm pretty sure you've already seen this). The value π is approximately 3.14.

Although the greek constant π is extremely useful for mathematics and circle graphs are very good for showing things like where your money is spent, nothing beats a real pie for throwing in someone's face!

Cheers,
Stephen La Rocque.