1. The return of materials or energy to a previous stage in a cyclic process. It is used to increase yields, to enrich a product, to conserve heat, and to improve operations.

2. The conversion of waste or used products to reusable material as a way of preventing the waste of potentially useful materials, reducing the consumption of fresh raw materials, reducing energy usage, and reducing pollution. Recycling is the third component of the ‘Reduce, Reuse, Recycle’ waste hierarchy.