In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium.

This includes:

1. electromagnetic radiation such as radio waves, visible light, and x-rays
2. particle radiation such as α, β, and neutron radiation
3. acoustic radiation such as ultrasound, sound
4. seismic waves.

Radiation may also refer to the energy, waves, or particles being radiated. Originally, radiation waves do not contain particles as they are transferred to Earth by the Sun for example.