PI (LETTER)

'Pi' (uppercase 'Π', lower case 'π') is the sixteenth letter of the Greek alphabet. In the system of Greek numerals it has a value of 80.
In Modern Greek, the name of the letter is pronounced ; in modern English, it is pronounced , in particular when referring to the mathematical constant (see below). In words, it is pronounced . In Modern Greek, the sequence of letters μπ represents the sound, as in ''boy'' (the second letter of the Greek alphabet is now pronounced as in ''very'').
The upper-case letter Π is used as a symbol for:

★ The product operator in mathematics, indicated with capital pi notation ∏ (in analogy to the use of the capital Sigma Σ as summation symbol).

★ In textual criticism, ''Codex Petropolitanus'', a 9th century, uncial codex of the Gospels, now located in St. Petersburg, Russia.

★ In legal shorthand, it represents a plaintiff.
The lower-case letter π is used as a symbol for:

★ The mathematical irrational constant 'π' ≈ 3.14159..., the ratio of a circle's circumference to its diameter in Euclidean geometry. The letter "π" is the first letter of the Greek words "περιφέρεια" 'periphery' and "περίμετρος" 'perimeter', ''i.e.'' the circumference.

★ The prime-counting function in mathematics.

★ Dimensionless parameters constructed using the Buckingham π theorem of dimensional analysis.

★ The osmotic pressure in chemistry. π=MRT

★ The elementary particle called the pi meson or pion.

★ Profit in microeconomics.

★ Inflation rate in macroeconomics.

★ A type of chemical bond in which the P-orbitals overlap

★ The natural projection on the tangent bundle on a manifold.
"Variant pi" or "pomega" ( or ϖ) is a glyph variant of lower case pi sometimes used in technical contexts as though it were a lower-case omega with a macron, though historically it is simply a cursive form of pi. It is used as a symbol for

★ The angular frequency of a wave in fluid dynamics (angular frequency is usually represented by $omega$ but this may be confused with vorticity in a fluid dynamics context).

★ The longitude of pericenter in celestial mechanics. [1]

★ Comoving distance in cosmology. [2]
In HTML, the capital letter Π can be produced using the codes Π or Π, and the lower-case by using π or π within the source code.