E regionn. See E layer.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.E region or E layern (General Physics) a region of the ionosphere, extending from a height of 90 to about 150 kilometres. It reflects radio waves of medium wavelength. Also called: Heaviside layer or Kennelly-Heaviside layer See also ionosphereCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014