Gamma

Gamma (uppercase/lowercase Γ γ), is the third letter of the Greek alphabet, used to represent the "g" sound in Ancient and Modern Greek. In the system of Greek numerals, it has a value of 3. Letters that came from it include the Roman C and Cyrillic Г.
In mathematics, the lowercase γ is used to represent Euler–Mascheroni constant, and the uppercase Γ is used to represent gamma function and gamma distribution. 
In physics, gamma rays (γ-rays) are a kind of radiation that result from nuclear decay. In the physics and engineering, gamma is used to represent many different things, depending on the subject.