(1) One of many high-polymeric substances, including both natural and synthetic products, but excluding the rubbers. At some stage in its manufacture, every plastic is capable of flowing, under heat and pressure if necessary, into the desired final shape. (2) Made of plastic; capable of flow under pressure or tensile stress. (Plastics Engineering Handbook of the Society of the Plastics Industry, Inc., edited by Michael L. Berins, 1991).