The energy transferred to material by the interaction of radiation. Dose is specified in joules per kilogram (or ergs per gram). The current S.I. unit of dose is the gray (Gy) which is 1 J /kg. The older unit, the RAD, has a magnitude of 100 erg/g and thus 1 rad = 0.01 Gy.
In the realm of radiation, there exists a parameter known as absorbed dose, measured in units of rad. This term denotes the amount of radiation energy that is extracted from an X-ray beam by an absorbing material.