This relates to the amount of energy actually absorbed in some material, and is used for any type of radiation and any material.
1 Gy = 1 m2s-2
Derived SI Unit, gray [Gy]
Defined as the absorbed dose in which the energy per unit mass imparted to the matter by ionizing radiation is 1 J/kg. Thus gray has units of J/kg.
The unit gray can be used for any type of radiation, but it does not describe the biological effects of the different radiations. Absorbed dose is often expressed in terms of hundredths of a gray, or centi-grays. One gray is equivalent to 100 rads.