Any of a subgroup of unstable mesons that consist of an electrically charged form with a mass 966 times that of an electron and a neutral form with a mass 974 times that of an electron, produced as a result of a high-energy particle collision. Also called K-meson. See Table at subatomic particle.
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.