Pi represents the ratio of the circumference of a circle to its diameter.

Pi is a number that will continue infinitely without a pattern.  It has been calculated to over 1-trillion digits beyond its decimal point!  So...we just refer to it as 3.14, which is why celebrate it on March 14th (3/14).

What will you do to celebrate Pi Day?  I suggest ordering a pizza...

Then, measure the circumference and diameter of the pizza.  Divide the circumference by the diameter.  While you calculate it out to, let's say, 50 digits... I'll eat the pizza.  Good times.