The absorbed dose is defined as:

The absorbed dose is defined as the energy absorbed per unit mass of material. This is an important concept in radiation physics, particularly in the context of understanding the biological effects of radiation on various tissues.

When radiation passes through a material, it transfers energy to that material. The absorbed dose quantifies this energy transfer in a way that is normalized for the mass of the material being irradiated. This is crucial since different materials will absorb energy differently based on their mass, and the dose provides a standardized measure that reflects the potential biological impact of the radiation.

For instance, if a certain amount of energy is absorbed by a specific mass of tissue, it allows us to assess the potential risk of damage to that tissue—whether it's healthy cells or cancerous cells. By focusing on the energy absorbed per unit mass, we can compare the effects of radiation across different types of materials and biological tissues, leading to better safety standards and treatment protocols in medical and safety contexts.

The other definitions provided do not capture the importance of mass in relation to energy absorption, which is the essence of the absorbed dose concept. The correct option directly addresses the relationship between energy absorption and mass, highlighting why it is essential for evaluating the effects of radiation exposure on health.