A rigid composite board of pressed cellulose, generally composed of wood chips or plant fibers, such as grass, reed, straw, bagasse, jute, flax, hemp, or recycled waste materials such as sawdust, bark, oat hulls, spent hops, newspaper and peanut shells. The fibers are compressed and bonded with heat and pressure. Many fiberboards are held together by the interlocking fibers and natural adhesives (wet process); other fiberboards have additional adhesive components such as urea formaldehyde resin, water glass, dextrin, asphalt, rosin, paraffin wax, plaster, and/or clay.

Source: AAT

http://vocab.getty.edu/page/aat/300014198