\▐rā-dē-▐ā-shәn\ n (15c) (1) Emission or transfer of energy in the form of electromagnetic waves or particles. (2) The electromagnetic waves or particles. NOTE − In general, nuclear radiations and radio waves are not considered in this vocabulary, only optical radiations, that is, electromagnetic radiations (photons) of wavelengths between the region of transmission to X-ray (1 nm) and the region of transition to radio waves (1 mm) (Serway RA, Faugh JS, Bennett CV (2005) College physics. Thomas, New York; Weast RC (ed) Handbook of chemistry and physics, 52nd edn. CRC Press, Boca Raton, FL).