Today is the 14th of March or 3/14, so happy International Pi Day! π or pi is a symbol which represents a constant in mathematics and it is the ratio of the circumference of a circle to its diameter. British mathematician William Jones came up with the symbol π in 1706. Since pi is irrational and its digits do not repeat, we simply use 3.14 as an approximation. To 10 decimal places, pi is 3.1415926535 as some of you might know.