Nu (/ˈnjuː/; uppercase Ν, lowercase ν; Greek: vι ni [ni]) is the thirteenth letter of the Greek alphabet, representing the voiced alveolar nasal IPA: [n]. In the system of Greek numerals it has a value of 50. It is derived from the ancient Phoenician language nun . Its Latin equivalent is N, though the lowercase (${\displaystyle \nu }$) resembles the Roman lowercase v.

The name of the letter is written νῦ in Ancient Greek and traditional Modern Greek polytonic orthography, while in Modern Greek it is written νι [ni].

Letters that arose from nu include Roman N and Cyrillic Н.

Like Mu, the uppercase Nu is normally identical to Latin N and is therefore not used internationally in scientific or mathematical contexts. The lower-case letter ν is used as a symbol for:

• Mathematics:
  • Degrees of freedom in statistics.
  • The greatest fixed point of a function, as commonly used in the μ-calculus.
  • Free names of a process, as used in the π-calculus.
  • One of the Greeks in mathematical finance, known as "vega".
  • The reciprocal of 1 plus the interest rate in finance.
  • The p-adic valuation or p-adic order of a number.
• Physics:
  • Kinematic viscosity in fluid mechanics.
  • The frequency^[1] of a wave in physics and other fields; sometimes also spatial frequency; wavenumber
  • The specific volume in thermodynamics.
  • Poisson's ratio, the ratio of strains perpendicular with and parallel with an applied force.
  • Any of three kinds of neutrino in particle physics.
  • The number of neutrons released per fission of an atom in nuclear physics.
  • Molecular vibrational mode, ν_x where x is the number of the vibration (a label).
  • The true anomaly, an angular parameter that defines the position of a body moving along an orbit (see orbital elements).
• Biology:
  • A DNA polymerase found in higher eukaryotes and implicated in translesion synthesis.
• Chemistry:
  • The stoichiometric coefficient.
• Psychology:
  • The maximum conditioning possible for an unconditioned stimulus in the Rescorla-Wagner model.

Look up Ν or ν in Wiktionary, the free dictionary.

• Movable nu
• Latin N, Latin V