Pi Approximation Day is observed every year on July 22 all around the world.

The fraction 22/7 is an approximate value of Pi, and there behind lays a specific reason why this day is observed on July 22. This day is celebrated on July 22 every year because the value of Pi is denoted by the fraction 22/7. Here, in the fraction 22/7 which denoted Pi, the numerator 22 symbolizes the date (22nd day of the month) and numerator 7 indicates the month (July).

Links:
Pi Approximation Day History, Meaning, Significance, other Celebration ideas