Plywood is a strong composite material made up of layers, also known as veneers, of wood which are glued together using heat and pressure as part of the bonding process. The layers are assembled so that the grain of the wood on one layer runs at right angles to the layers above and below it.

Sometimes viewed as the original engineered wood, plywood is usually made up of an odd number of layers, three or more, which ensures that the grain on the outermost layers runs in the same direction.

The multiple layer construction and the alternating grain direction give plywood its dimensional stability and help it to resist warping, cracking, shrinkage, and breakage. These attributes and its generally high degree of strength are common reasons for its wide use. It has replaced many dimensional lumbers on construction applications for these reasons.