A plank of wood is a long, flat piece of wood that is usually rectangular in shape. It is often used in construction and carpentry, as well as for furniture and other items. The term 'plank of wood' can also be used to refer to a BOARD, which is a five-letter word for the same object. A BOARD is typically thicker than a plank and is used for a variety of purposes, such as flooring, siding, and decking.