Today is March 14th, or in the American system of time and date notation 3.14.
the numbers 3, 1 and 4 just happen to be the first three numbers of Pi (π), a mathematical constant denoting the ratio of a circle’s circumference to its diameter.
Pi Day was first celebrated in the United States after being founded in 1988 by the late Larry Shaw, formerly an employee of the Exploratorium science museum in San Francisco. Celebrations often involve either eating pie or holding Pi recitation competitions, or both.
Image courtesy of Wikimedia Commons
Besides Pi Day, some people also celebrate Pi Approximation Day on 22nd July (22/7).