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 consists of photons, such as radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, and gamma radiation (γ)
• particle radiation consists 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, dependent on a physical transmission medium
• gravitational radiation, in the form of gravitational waves, ripples in spacetime