Gamma (upper case Γ, lower case γ) is the third letter of the Greek alphabet. In the system of Greek numerals it has a value of 3.

It gives its name to several things:

• Gamma characteristic power law, and gamma correction in photography, television and computer display systems. Gamma is the exponent in a power-law relationship between video or pixel values and the displayed brightness. In photography it is the slope of the curve of (density or log(opacity)) of the film image versus log(exposure) (the Hurter-Driffield curve), in the straight line region.
  
• In the game of Tetris, gamma is another name for the J tetromino.
  
• 1 gamma is a unit of magnetic flux density, 1 gamma = 10−9 tesla or 1 nanotesla.
  
• E-102 Gamma is a fictional character in the Sonic the Hedgehog universe.
  
• Gamma is a giant peace-keeping robot stolen by Dr. Wily which is the final boss of Capcom's Nintendo game Megaman 3.
  

The upper-case letter Γ is used as the symbol for:

• The gamma function (related to factorials) in mathematics.
  
• The Gamma distribution in probability theory and statistics.
  
• The symbol for Γ is used on the hat of the videogame character Waluigi
  
• The reflection coefficient in electrical engineering.
  
• Gamma is the third caste in Aldous Huxley's dystopic satire Brave New World.
  
  

The lower-case letter γ is used as the symbol for:

• The Euler-Mascheroni constant in mathematics.
  
• A risk management measure in mathematical finance.
  
• The photon, seen as an elementary particle in physics.
  
• Gamma rays in physics and astronomy.
  
• The gamma factor in relativity theory and astronomy.
  
• The adiabatic index of a gas in physics. Often the letter kappa κ is used.
  
• The propagation constant of an electromagnetic wave (in electrical engineering and electromagnetic theory).
  
• The third brightest (usually) star in a constellation. See Bayer designation.
  

Letters that arose from Gamma are the Roman C and G and the Cyrillic letter Ghe.