This document discusses different types of radiation and their effects. It describes: 1) Radiation is the transfer of energy through space or matter. It includes electromagnetic radiation like radio waves and x-rays. 2) Humans and organisms are exposed to both ionizing radiation, which can damage cells, and non-ionizing radiation like infrared light, which has weaker thermal effects. 3) Ionizing radiation comes from natural sources like cosmic rays and radioactive elements in the ground, as well as man-made sources like nuclear weapons, power plants, medical imaging, and nuclear accidents.