1. The taking in, incorporation, or reception of gases, liquids, light, or heat.

2. In psychology, devotion of thought to one object or activity, with inattention to others.

3. In radiology, the uptake of energy from radiation by the tissue or medium through which it passes.4. In radiation or medical physics, the number of disintegrations per second of a radionuclide.

5. in chemistry, the penetration of a substance within the inner structure of another.