As we celebrate again in 2018, here are some Pi Day facts you should know. What Is Pi? Pi represents the ratio of a circle’s circumference to its diameter.

The misconception that it's a variable comes in part from the fact that we often express circumference and area in terms of Pi.

Time is a flat circle, Matthew McConaughey tells us, neglecting to explain how then we could measure time's circumference to derive its diameter, using pi. (Maybe it's best not to take the ...

What is Pi Day, and why do we celebrate it every March 14? Here's what to know as math lovers around the world mark Pi Day.