Layers of wood, also known as plies, are thin sheets of wood that are glued together to form a thicker material. Plies are often used in the construction of furniture, flooring, and other woodworking projects. The number of plies used can vary depending on the desired strength and stability of the finished product. Plies are also used in the production of plywood, which is a type of engineered wood made from multiple layers of wood veneer.