I/Oabbr. input/outputAmerican 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.I/O abbreviation for (Computer Science) input/output Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014I?o (?a? o?, ?i o?) n. 1. (in Greek myth) a woman loved by Zeus and changed by him into a heifer, which Hera claimed and put under Argus’ guardianship. 2. a large volcanically active moon of Jupiter. Io. Iowa. I/O Computers. input/output. I.O. or i.o., indirect object. Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.