**Pi (letter)**

From Wikipedia, the free encyclopedia.

**Pi** (Π π) is the 16th letter of the Greek alphabet and has a numeric value of 80. In words it is pronounced /p/.

The upper-case letter Π is used as a symbol for:

- The product operator in mathematics (similar to a series).
- In textual criticism,
*Codex Petropolitanus*, a 9th century, uncial codex of the Gospels, now located in St. Petersburg, Russia.

- The mathematical constant &pi 3.14159, being the ratio of a circle's circumference to its diameter.
- The prime counting function in mathematics.
- The pi mesons in particle physics.
- Profit in economics.