What is the difference between denim and non denim jeans?

The basic difference between denim and non-denim jeans is as follows:

Denim fabric's yarns are dyed before weaving the fabric. However, In Nondenims the greige yarns are woven and then greige fabric obtained is called RFD (ready for Dying), PFGD (Prepared for Garment dying) and Non denims. it could be any weave or twill.