A unit for absorbed dose equal to the amount of energy from any type of ionizing radiation (e.g., alpha, beta, photons, neutrons, etc.) deposited in any medium (e.g., water, tissue, air). A dose of 1 rad means the absorption of 100 ergs per gram of absorbing tissue (100 rad = 1 Gy). The term is the commonly used contraction of radiation absorbed dose. This energy density value is a purely physical characterization of the radiation received without regard to biological effects. The number of rads of radiation becomes more meaningful when its effects on living tissue are considered. Hence, there is a process of converting the number of rads to what is meaningful for living tissue, taking into account the type of tissue and type of radiation. See also equivalent dose, quality factor, and sieverts.