flat-pack

adjective

(of a piece of furniture, equipment, or other construction) supplied in pieces packed into a flat box for assembly by the buyer

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