What does the term 'density' refer to in radiology?

In radiology, the term 'density' specifically refers to the amount of darkness seen on a radiograph. This darkness is a result of the degree to which x-rays have been absorbed by the tissues in the body and the film's exposure to radiation. When more radiation penetrates a structure and hits the film, it results in darker areas on the radiograph. Conversely, less radiation absorption leads to lighter areas. Thus, density is directly tied to how various tissues absorb x-rays; denser materials, like bone, absorb more x-ray radiation and appear lighter on the film, while less dense materials appear darker.

This understanding is crucial in radiology as it helps in interpreting images by indicating the presence of normal or abnormal structures based on their radiographic density.