No, not the Blueberry or Apple type, but Pi, the 16th letter of the Greek Alphabet Day.  In mathematics, it serves as the symbol for the ratio of the circumference of a circle to its diameter. Pi is a transcendental number, meaning it will repeat infinitely without ever appearing exactly the same. Pi has been calculated to over 51 billion decimal places with the use of computers. However Pi is usually calculated to 3 digits, 3.14. Therefore, March 14 is Pi day.