Pi Day is a non-religious holiday celebrating the number pi. It is celebrated on March 14 (3/14 in month/day format), which looks like the first 3 numbers of Pi, 3.14.
Creation
It was created in 1988 by Larry Shaw. It is mainly held at San Francisco Exploratorium, where Shaw worked as a physicist.
Celebration
A Pi Pie with the first 28 digits of Pi.
There are many ways to celebrate Pi day. Some people eat Pi Pie and discuss the relevance of Pi. Schools celebrate by putting up decorations or giving students Pi-Related Math Problems. Some Schools also put Math Night on this day as a token to Pi.