pi

Pi is a Greek letter written "π".

Pi is a number that is found by dividing the circumference of a circle by its diameter. Pi is constant, it is always the same (close to 3.14159, also accurate approx as tfrac 355 113, or rough approx as tfrac 22 7). It is usually written as "π"

Example: The distance around a circle is twice the radius times pi; C = 2πr.