What is pi? What is pi used for?

Pi is a mathematical term used to describe the ratio of the circumference of a circle to its diameter. The area of a circle is equal to π times the square of the length of the radius, or πr2. So πr2 = The area of any circle. Since pi is non-repeating and non-terminating, it is often approximated as 22/7 or 3.14. To make calculations even easier, it is often rounded to 3.1416.