Secondary or incidental products that are created during the processing or manufacturing of a main product. 

• By-products are typically a subset of processed products or manufactured products. 

• When by-products are marketable, their market value is small in relation to the value of the main product. When processing or manufacturing results in multiple products with significant market value (eg, beef and leather from cattle, or soymeal and soy oil from whole soybeans), these are not considered by-products.