APPabbr. amyloid precursor proteinapp (?p)n. A computer application.[Short for application.]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.app (æp) n (Computer Science) computing (esp downloaded to a mobile device) short for application programCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014app (æp) n. Computers (informal). an application program; application software. [1985?90] app. 1. apparatus. 2. apparent. 3. appendix. 4. applied. 5. appointed. 6. approved. 7. approximate. Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.