A polymer is a molecule that has a very long chain of monomers, which can be defined as a single part of the molecule that repeats itself throughout a polymer. So the union of many monomers results in a polymer. For example, the PVC (polyvinyl chloride) has the following monomer:
When this monomer repeats itself, the resulting chain has the following denotation:
Where n = the number of times vinyl chloride repeats in the polymer structure
For this reason of being a very long-chain molecule, polymers have specific properties such as high resistance to heat, they can be flexible or tough, and they can conduct electricity or not; every property depends on the polymer and its structure. So plastics, besides other commonly used materials, are an example of a polymeric material and are usually referred to as a polymer.