Meaning of “radiation” - Learner’s Dictionary

radiation

noun [ U ] uk us /ˌreɪdiˈeɪʃən/
HARMFUL ENERGY

a form of energy that comes from a nuclear reaction and that in large amounts can be very dangerous:

dangerously high levels of radiation
radiation sickness
HEAT

energy from heat or light that you cannot see:

solar/microwave radiation

(Definition of “radiation” from the Cambridge Learner’s Dictionary © Cambridge University Press)