ASCII Character πGreek small letter pi
Pi /ˈpaɪ/ (uppercase Π, lowercase π and ϖ; Greek: πι [pi]) is the sixteenth letter of the Greek alphabet, representing the voiceless bilabial plosive IPA: [p]. In the system of Greek numerals it has a value of 80. It was derived from the Phoenician letter Pe (Phoenician pe.svg). Letters that arose from pi include Latin P, Cyrillic Pe (П, п), Coptic pi (Ⲡ, ⲡ), and Gothic pairthra (𐍀). The lowercase letter π is used as a symbol for the mathematical real transcendental (and thus irrational) constant π ≈ 3.14159..., the ratio of a circle's circumference to its diameter in Euclidean geometry.