n (1) A heavy weight, thick sheet of paper or other fibrous substance, usually of a thickness greater than 6 mm (0.006 in.). (2) Lumber less than 2 in. (6 cm) thick and between 4 in. (10 cm) and 12 in. (30 cm) in width; a board less than 4 in. (10 cm) wide may be classified as a strip.