What is a polymer? What can we say about the molecular mass of a polymer? In which four industries are polymers mostly used?

(N/A) The word 'polymer' is derived from two Greek words: 'poly' meaning many and 'mer' meaning unit or part.
$A$ polymer is defined as a very large molecule (macromolecule) formed by the joining of repeating structural units on a large scale.
Polymers possess a very high molecular mass,typically in the range of $10^{3} - 10^{7} \ u$.
Polymers are the backbone of four major industries: $1.$ Plastics,$2.$ Elastomers,$3.$ Fibres,and $4.$ Paints and varnishes.