Pi ( π ) is one of the mathematical constants classified as irrational number. An irrational number has a value wherein the actual last digit is unknown. It is commonly used in mathematical equations as a ratio of circumference to diameter.

For those who don't know, July 22 is also known as Pi Approximation Day. This is because 22/7 is a common approximation of pi. Pi-Day is actually observed on March 14 simply because the first three digit of pi is 3.14 which is commonly used for computation. To celebrate the day and mathematicians across the world, Google has come up with an excellent Google Doodle last year (March 14, 2010). The image on this article shows the exact doodle used by Google. Now who knows what would happen as mathematicians celebrates another Pi day on March 14, 2015 (03-14-15) :p

The value 22/7 on the other hand is an apporximation of the said mathematical symbol that is celebrated every July 22. Though the said fraction is not equal to pi itself and only accurate up to the first two decimal places of the said symbol (22/7 is 3.14285714 while pi is 3.1415929204...). Chinese actually found a better approximation though which is 355/113 also called as Milü ( 22/7 has been given the name Yuelü ).

As to what the exact value is the exact value of pi, even I don't know and have no intention of knowing the other digits (the only value I know are up to 5 which is 3.1416 :p )... Happy Pi Approximation Day!

By the way, do you know that there are also dates called Square Root Day? :)