Gamma the third letter of the Greek alphabet, written as Γ, in its uppercase form, and γ in lowercase. In Greek, it is called "ghamma" and either has a guttural sound like the French "r", which does not exist in English and is represented by the letters "gh", or a "y".
Gamma in physics
γ is used to indicate both gamma rays, a type of electromagnetic radiation with a very short wavelength, and the photon.