Pi, Greek letter (π), is the symbol for the ratio of the circumference of a circle to its diameter. Pi Day is celebrated by math enthusiasts around the world on March 14th. (in the mm/dd date notation: 3/14); since 3, 1 and 4 are the first three digits of π. March 14 is also the birthday of Albert Einstein and the two events are sometimes celebrated together. Pi = 3.1415926535…

With the use of computers, Pi has been calculated to over 1 trillion digits past the decimal. Pi is an irrational and transcendental number meaning it will continue infinitely without repeating. The symbol for pi was first used in 1706 by William Jones, but was popular after it was adopted by the Swiss mathematician Leonhard Euler in 1737.

There are a large variety of ways of celebrating Pi Day and most of them include eating pie and discussing the relevance of π. The first Pi Day celebration was held at the San Francisco Exploratorium in 1988, with staff and public marching around one of its circular spaces, then consuming fruit pies. The museum has since added pizza to its Pi Day menu. The founder of Pi Day was Larry Shaw, a now-retired physicist at the Exploratorium who still helps out with the celebrations.

The Massachusetts Institute of Technology often mails its acceptance letters to be delivered to prospective students on Pi Day.