Today is pi Day (march 14 or 3/14). Which is more celebrated now than March 15 or the Ides of March, the day Julius Caesar was killed. Of course it's not as celebrated as St. Patrick's day everywhere but in Ireland itself.
Pi is the ratio of the circumference of a circle to its diameter. It is used to calculate the area of a circle, the circumference of a circle, and the volume of a sphere. It is also used in the famous normal distribution in statistics, aka the bell shaped curve as seen in the formula below. Here the probability value of x is conditioned on the variables mean mu and variance sigma squared. Pi is a constant in this equation.