Radiation is energy emitted by matter in the form of electromagnetic waves or subatomic particles. Depending on its energy level, radiation can be classified as ionizing or non-ionizing. Ionizing radiation has sufficient energy to detach electrons from atoms or molecules, converting them into ions, which can be harmful to living organisms. Sources of ionizing radiation include radioactive materials emitting alpha, beta, or gamma rays, X-rays from medical examinations, and various particles in cosmic rays interacting with Earth's atmosphere.