In mathematics, π (pronounced "pi") is a special symbol representing pi. It is an irrational number and its approximate value is about 3. 14 159. π is a very important and widely used constant in mathematics, which is associated with a circle.

Mathematicians usually use the Greek letter π to represent pi. Pi is defined as the ratio of the circumference of a circle to its diameter, that is, π is equal to the circumference of a circle divided by its diameter. No matter what the diameter of a circle is, the value of pi is always the same. Therefore, π is a constant.

The exact value of π is an infinite acyclic decimal and cannot be accurately expressed as a finite decimal. So in practical application, people usually use the approximate value of π to calculate. In the field of computer science and engineering, the approximate value of π is usually expressed by 3. 14 159 or more decimal places.