Pi (letter)

Pi (uppercase Π, lowercase π) is the sixteenth letter of the Greek alphabet. In the system of Greek numerals, it has a value of 80.

In mathematics, the lowercase π most commonly represents the mathematical constant approximately equal to 3.14159, defined as the ratio of a circle's circumference to its diameter. This use is widespread and fundamental across numerous areas of mathematics, physics, and engineering. The uppercase Π is frequently used as a notation for a product of a series of terms, analogous to the use of Σ for summation.

Beyond mathematics, the letter π is used in various other fields. In physics, it can represent a pion, a type of subatomic particle. In economics, it is sometimes used to denote profit. In statistics, it can represent a population proportion or probability.

The symbol's visual representation consists of two vertical strokes connected by a horizontal stroke at the top, resembling a stylized gateway. Its origin is believed to be derived from a Phoenician letter, and its form has remained relatively consistent throughout its history.