In the US dates are expressed MM-DD-YY.
Looking at just the month and day and using a period as a separate we get 03.14 which is a rough approximation for the value of the irrational number π (PI).
The pronunciation of the number π sounds identical to the word Pie.
So, that’s why March 3 is called “Pie Day.”
The perfect π day was March 3, ’15 which displays as 3.1415.
On that day was the perfect π time was 9:26:53 which displays as 3.14153.141592653, a much more significant approx of “π”.