excerpt from article  http://www.cute-calendar.com/event/pi-day/6374-world.html

Photo courtesy of: dmcpress.org

Pi Day and Pi Approximation Day are two unofficial holidays held to celebrate the mathematical constant π (pi). Pi Day is celebrated on March 14, or in the month/day date format as 3/14; since 3, 1 and 4 are the three most significant digits of pi. March 14 is also the birthday of Albert Einstein so the two events are sometimes celebrated together. Pi Approximation Day is held on July 22, or in the more common day/month date format as 22/7, which is an approximate value of pi….

… There is a large variety of ways of celebrating Pi Day and most of them include eating pie and discussing the relevance of pi. Pi Day is often celebrated with pies, given that pi and pie are homophones.