The absorbed dose is defined as:

The absorbed dose is defined as the energy absorbed per unit mass of material. This measurement is crucial in fields such as medical physics, radiation therapy, and radiation safety because it quantifies the amount of energy deposited in a substance (like human tissue) due to exposure to ionizing radiation. The absorbed dose is typically measured in grays (Gy), where one gray corresponds to the absorption of one joule of radiation energy by one kilogram of matter.

Thus, the correct answer reflects the fundamental concept of how energy interacts with mass in the context of radiation exposure, highlighting the importance of knowing how much energy is actually absorbed by the material in question. Other definitions of energy or mass do not capture the specific relationship that the absorbed dose represents.