Today is Pi Day! What is the importance of pi? It's the ratio between a circumference and diameter of a circle. So why is today Pi Day? Because today is 3/14 (in America that is). And the first digits of pi are 3.14, so that's the explanation. On the other hand, pi is also infinite, so it has no end. The only digits of pi that I know are 3.1415926535897932384626433832795028841971693993751058209749445923.