Radiation
In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or a material medium. This includes: electromagnetic radiation consisting of photons, such as radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, and gamma radiation (γ) particle radiation consisting of particles of non-zero rest energy, such as alpha radiation (α), beta radiation (β), proton radiation and neutron radiation acoustic radiation, such as ultrasound, sound, and seismic waves, all dependent on a physical transmission medium gravitational radiation, in the form of gravitational waves, ripples in spacetime Radiation is often categorized as either ionizing or non-ionizing depending on the energy of the radiated particles.