The American Heritage® Dictionary of the English Language, 4th edition Copyright © 2010 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
noun (used with a sing. verb)
The branch of physics that deals with phenomena associated with magnetic effects on matter as it emits light. It has been used to develop a data-storage technique in computer applications.