\piThe Greek letter Pi (\pi) is commonly used in mathematics and science to represent the mathematical constant approximately equal to 3.14159, which is the ratio of a circle's circumference to its diameter. It is also used to denote a product of a sequence.
Circumference of a circle with radius r.
C = 2 \pi rArea of a circle with radius r.
A = \pi r^2Approximation of the mathematical constant Pi.
\pi \approx 3.14159