There are a few different theories out there about why pi is called pi, but the most likely explanation is that it’s simply a shortened version of the Greek word “periphery.” This makes sense, since one of the most common uses for pi is to calculate the circumference (or periphery) of a circle. So there you have it! Pi has been with us for centuries, and will continue to be an important part of math and science for many years to come. Thanks for asking!