Plastic is the general common term for a wide range of synthetic or semisynthetic organic solid materials suitable for the manufacture of industrial products. Plastics are typically polymers of high molecular weight, and may contain other substances to improve performance and/or reduce costs.
The word derives from the Greek πλαστικός (plastikos), “fit for molding”, from πλαστός (plastos) “molded”  . It refers to their malleability, or plasticity during manufacture, that allows them to be cast, pressed, or extruded into an enormous variety of shapes—such as films, fibers, plates, tubes, bottles, boxes, and much more.
The common word “plastic” should not be confused with the technical adjective “plastic”, which is applied to any material which undergoes a permanent change of shape (a “plastic deformation”) when strained beyond a certain point. Aluminum, for instance, is “plastic” in this sense, but not “a plastic” in the common sense; while some plastics, in their finished forms, will break before deforming — and therefore are not “plastic” in the technical sense.
more at: en.wikipedia.org/wiki/Plastic