quantum electrodynamics

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The quantum theory of the electromagnetic interaction and the properties and behavior of electrons, positrons, photons, and the electromagnetic field.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun physics the study of the interaction of electromagnetic radiation with electrically charged matter within the framework of relativity and quantum mechanics

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a relativistic quantum theory of the electromagnetic interactions of photons and electrons and muons