A day for celebrating Pi – the ratio of a circle’s circumference to its diameter.
Pi Day is celebrated in a variety of ways. Parties or other observances may be held by mathematics departments in educational institutions. Harvard’s Math department, for instance, has a pi recitation contest as well as a pie eating contest. Mathematics or science clubs might gather to consider the role that the number pi has played in their lives and to imagine the world without pi. During such an event, pi celebrants may approximate pi, devise alternative values for pi, eat pie, play pinata, drink Pina Colada, eat pizza (which itself is called pizza pie), listen to the song “Pi” by Kate Bush, watch Pi, or recite Pi. The song 867-5309/Jenny is sometimes sung, replacing the digits with the first several digits of pi.*
*source: wikipedia – Pi Day