what is pi math
The number Ï is a mathematical constant, the ratio of a circle 's circumference to its diameter, commonly approximated as 3.14159. It has been represented by the Greek letter  Ï  since the mid-18th century, though it is also sometimes spelled out as  pi  (/paÉª/).he symbol used by mathematicians to represent the ratio of a circle's circumference to its diameter is the lowercase Greek letter Ï, sometimes spelled out as pi. In English, Ï is pronounced as pie (/paÉª/ , paÉª).