3.14 - 14 March
is coming in
PI DAY - 3.14
In the US dateformat month comes before day, so 14 March is written 3.14 - and it's therefore called PI day.
By conincidence this date also happens to be the date of birth of Albert Einstein in 1879.
While PI is a constant with an unlimited number of decimals for maximum accuracy, a more inaccurate number is sometimes used in simple math to get close to the real PI: 22/7.
22/7 is only accurate down to 2nd decimal, yet it also has it's own day: The PI Approximation Day on 22/7.