The term “plastics” is used to describe a wide variety of resins or polymers with different characteristics and uses. Polymers are long chains of molecules, a group of many units, taking its name from the Greek “poly” (meaning “many”) and “meros” (meaning “parts” or “units”).
The term “polymer” is often used as a synonym for plastic, but many other types of molecules — biological and inorganic — are also polymeric. While all plastics are polymers, not all polymers are plastic. Polymers are rarely useful in themselves and are most often modified or compounded with additives (including colours) to form useful materials. The compounded product is generally termed a plastic. Most people have little contact with "polymers" because most articles that they come across are actually modified and coloured and therefore are actually plastics. Polymers can be classified in many ways, based on how they are developed and perform. For this discussion of recycling, an understanding of two basic types of polymers is helpful: