Happy Pi Day! and What is Tau?

π (sometimes written as "pi") is a special number representing the ratio (relationship) of any circle's circumference (distance around) to its diameter (distance across). π is approximately equal to 3.14159265 but the real decimal version of π contains at least 5 trillion digits.

Pi is (still) wrong.

Tau versus pi: Why Tau might be a better number to look at than Pi