Fibreboard is a board made from wood fibres pressed together, usually with glue, into a cheap, flat sheet. Builders use it in furniture and cheap walls: the back of a wardrobe, a cupboard door, a panel. It is not a solid plank, and it swells if it gets wet. MDF is one common kind — smooth and dense. British spelling keeps the re in fibre; American English writes fiberboard. Same material. In Taiwan shops you may hear 密集板; that usually means MDF, one kind of fibreboard, not every kind.