n.1.a wood or metal receptacle placed on a desk to hold incoming material requiring attention, especially documents.Webster’s Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.
in box
in? box` n. a traylike receptacle in an office for incoming documents. Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.