**Pi is the ratio of a circle's circumference to its diameter.** The number pi, symbolized by a Greek letter, has a constant value that approximately equals 3.14. The distance around any circle when divided by its diameter always gives this exact result.

This constant is commonly used to solve the area of a circle, with the formula "pi r^2“ or the product of pi and the square of the length of the radius. Pi is an irrational number, which means it cannot be expressed as a common fraction, and it has an infinite decimal representation without any repeating pattern. The rounded version of pi is accepted for general computations. Pi up to 20 decimal digits is 3.14159265358979323846.