Roentgen refers to a unit of measurement for ionizing radiation exposure in air. It quantifies the amount of radiation that produces a specific amount of ionization in a given volume of air. This unit is essential in fields like radiology and nuclear medicine, where understanding radiation levels is crucial for safety and effective treatment. The term is named after Wilhelm Conrad Roentgen, a German physicist who discovered X-rays in 1895. His groundbreaking work laid the foundation for modern imaging techniques, allowing doctors to visualize the internal structures of the body without invasive procedures.