Definition of gamma ray

1) High energy electromagnetic radiation. A highly penetrating type of nuclear radiation similar to x-ray radiation, except that it comes from within the nucleus of an atom and has a higher energy. Energywise, very similar to cosmic ray except that cosmic rays originate from outer space. For more information see Electrochemistry

2) Extremely short wavelength and intensely high-energy electromagnetic radiation. Gamma rays originate from an atom's nucleus and normally accompany alpha and beta particles as part of the emissions of the radioactive decay of an atom and always accompany nuclear fission. Because gamma rays are energy and not matter, they are very penetrating and can cause damage to animal and plant tissues. Gamma rays are absorbed by extremely dense materials like lead (Pb) and depleted uranium (U).