Nylon is a polymer, a plastic with super-long, heavy molecules built up, in short, endlessly repeating sections of atoms, just like a heavy metal chain is made of ever-repeating links.
Nylon is not actually one, single substance but the name given to a whole family of very similar materials called polyamides.
Nylon polymers are condensation polymers. They are not homopolymers because some of the groups are also copolymers. e.g. Nylon $$6,6$$.