The term tongue and groove comes from the fact that the flooring is milled to have
a "tongue" edge that fits into the "groove" edge of the piece next to it when installed. The joint allows for the natural contraction and expansion of the wood with humidity and temperature. Plank style antique wood flooring is cut with the grain of the wood and can be in lengths from a few feet to 12 feet or more. Wood "moves" with changes to environment by becoming narrower, not shorter in length, so the tongue and groove joint is designed to allow for this contraction. The potential width and length of a board is obviously only limited from the source where is comes from.