Pi Day is a national holiday celebrating the mathematical constant Pi. It is observed on March 14. The date comes from the first three digits of Pi (3.14), with some people beginning their celebration at 1:59:26 (the following digits 3.1415926). Celebrations often involve eating pie, cookies or some other circular delicacy. Many Elementary and Middle School teachers use March 14 to introduce their students to the concept of Pi. People also hold pi memorization contests to see who can recite the most digits of pi from memory. The world record for memorization is over 67,000 digits!
Pi Approximation Day is a similar festival, celebrated on 22nd July (European date format) since the fraction 22/7 is commonly used as a very approximate value for Pi.