quantum electrodynamics, QED(noun) a relativistic quantum theory of the electromagnetic interactions of photons and electrons and muons. QED(Noun) Quantum electrodynamics. QED(Interjection) Quod erat demonstrandum (Latin what had to be proved or what was to be demonstrated). QED. QED were an Australian New Wave trio, whose lead singer, Jenny Morris, went on to achieve commercial success as a solo artist.