a double pleat, with the material folded under at each side.
Origin of box pleat
First recorded in 1880–85
Also called box plait.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
a flat double pleat made by folding under the fabric on either side of it
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012