What is the pie sign use for?

The pie sign (🥧) is the mathematical symbol for pi, which is the ratio of a circle's circumference to its diameter.

Pi is an irrational number, meaning it cannot be expressed as a simple fraction or decimal; the number goes on forever, with more digits added without any repeating pattern. Pi is important in many areas of mathematics, physics, and engineering, particularly those involving circles. Its most popular form of expression is 3.14.