plywood -
Construction material supplied in sheets, and made of three or more layers of woodveneer glued together, laid up with alternating layers having their grain perpendicular to each other.
plywood -
A specific grade or type of this construction material.
Wikipedia
Plywood is a type of manufactured wood made from thin sheets of wood. The layers are glued together so that adjacent plies have their wood grain at right angles to each other for greater strength. There are an odd number of plies, as symmetry makes the board less prone to warping.