Pi Day is a holiday commemorating the mathematical constant π (pi). Pi Day is celebrated on March 14 (or 3/14 in month/day date format), since 3, 1 and 4 are the three most significant digits of π in the decimal form. In 2009, the United States House of Representatives supported the designation of Pi Day. Pi Approximation Day is held on July 22 (or 22/7 in day/month date format), since the fraction 22⁄7 is a common approximation of π.
The Greek Mathematician Archimedes first approximated Pi as roughly 3.14. However, the fraction 22/7 has been found to be a closer approximation of Pi than 3.14. Thus many scientists choose to celebrate Pi Day on July 22.
Once one gets started on the celebrations, why stop at a day? The Pi minute is also celebrated and occurs twice on each Pi Day. This stems from a more accurate value of Pi being determined to be 3.1415926... Thus on March 14 at 1:59:26 a.m. and 1:59:26 p.m. we have the Pi Day's minutes and seconds occurring.
"So Wish U a Happy Mathematical Pi Day"
[Courtesy: Wikipedia & The Hindu]