Radiation is a phenomenon wherein energy is propagated and emitted in the form of electromagnetic waves. Radiation consists of different types of waves - water waves, sound waves, light waves, and heat waves. A burning candle emits radiation in the form of heat and light.
Radiation can be classified into two major categories - ionizing radiation and non-ionizing. Ionizing radiation produces charged particles/ions in matter, and is produced by unstable atoms. Unstable atoms possess excess energy or mass, or both. Ionizing radiation can also be produced by high-voltage devices such as x-ray machines. X-ray, gamma, alpha, beta, and neutron radiation are examples of ionizing radiation.
Non-ionizing radiation is said to possess enough energy to move around atoms in a molecule or cause them to vibrate, but not enough to remove electrons. Radio waves, microwaves, heat or visible light are examples of non-ionizing radiation.
The shorter the wavelength of the wave radiation, the more energy it carries, x-rays and gamma rays are more energetic than light. They penetrate much deeper into all kinds of matter, and they produce much greater effects, and hence are considered harmful. Prolonged exposure to ionizing radiation can damage living tissue in the human body.
Radiation is widely used in medicine, communication, and science.