Real Dictionary

radiation
uncountable noun: Radiation consists of very small particles of a radioactive substance. Large amounts of radiation can cause illness and death.

radiation in American English
the act or process of radiating; specif., the process in which energy in the form of rays of light, heat, etc. is sent out through space from atoms and molecules as they undergo internal change
noun: the process in which energy is emitted as particles or waves

radiation in British English
noun: the emission or transfer of radiant energy as particles, electromagnetic waves, sound, etc

radiation in Chemical Engineering
noun: Radiation is the flow of heat from one surface to another by infrared waves (= waves with a longer distance between them than waves of visible light).

radiation in Mechanical Engineering
noun: Radiation is the flow of heat from one surface to another by infrared waves.