Pi (letter)

Pi (upper case Π, lower case π) is the 16th letter of the Greek alphabet. In the system of Greek numerals it has a 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 lower-case letter π is used as a symbol for:

• The mathematical constant π ≈ 3.14159, the ratio of a circle's circumference to its diameter.
• The prime counting function in mathematics.
• The pi mesons in particle physics.
• Profit in microeconomics.
• Inflation rate in macroeconomics.