Synthetic fibres are man-made fibres which are made up of small units which are joined together. These units are made of chemical substances. Such small units combine to form a large single unit called a polymer. Hence, a polymer is made of many repeating units. Polymers also occur in nature.
Example:  Rayon and Nylon are synthetic fibres. Rayon is obtained by the chemical treatment of wood pulp or cellulose. Nylon is the first fully synthetic fibre. It was prepared from coal, water and air.