'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
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.