Slang any of a group of young people in the U.S. loosely organized in 1968 as radical activists
Webster’s New World College Dictionary, Fourth Edition, compiled by the
editors of Webster’s New World Dictionaries. Copyright © 2010 by Houghton
Mifflin Harcourt. Published by Houghton Mifflin Harcourt. All rights reserved.
Word origin of 'yippie'
< Y(outh) I(nternational) P(arty),
a supposed, but nonexistent group + hippie