Dictionary.com
definitions

box pleat

noun
  1. 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. 2018
British Dictionary definitions for box pleat

box pleat

noun
  1. 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