Radiation is energy emitted from a “body” as either waves (so-called “electromagnetic radiation”) or as particles. There are many different types of radiation, and only some are harmful.
The electromagnetic spectrum, for example, is divided up according to wavelength, from long wavelength electromagnetic radiation like microwaves and radio waves, through infrared radiation, visible light, ultraviolet light, to short wavelength X-rays.
Alpha and beta radiation consists of radioactive particles. Naturally-occurring radon gas, for example, emits alpha particles.
