π is the ratio of a circle's circumference to its diameter. It shows up anywhere circles, waves, or periodicity appear — geometry, physics, signal processing, probability.
22/7 is an old, handy approximation. It equals 3.142857 142857 …, repeating the block 142857 forever. It agrees with π to only two decimal places, but it is close enough for many hand calculations.
The real π is irrational — its decimal expansion never repeats and never terminates. So while this page will happily compute 22/7 forever, no finite fraction can ever equal π itself.
A better rational approximation is 355/113, accurate to seven digits. Ancient mathematicians in China, Greece, and India all searched for closer values — a hunt that continues today, now measured in trillions of digits.
fun fact — 142857 is a cyclic number: multiply it by 1..6 and you get the same digits in a different rotation.