**The number Pi, symbolized by a Greek letter, has a constant value that approximately equals 3.14159.** 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.

Pi, by definition, is the ratio of a circle’s circumference to its diameter (Pi = C/d). This constant is used to solve the area of a circle, with the formula “Pi r squared” or “the product of Pi and the square of the length of the radius.” The rounded-off version of Pi is accepted for general computations. Here’s Pi up to 20 decimal digits: 3.14159265358979323846.