1. something produced in a usually industrial or biological process in addition to the principal product
2. a secondary result or consequence that occurs in addition to the intended outcome

Examples

• The factory produces steel as its main product and slag as a byproduct.
• Sawdust is a common byproduct of lumber mills.
• Carbon dioxide is a byproduct of cellular respiration.
• The new policy had several unexpected byproducts.
• Cheese production creates whey as a valuable byproduct.
• Economic growth often has environmental byproducts.
• The oil refinery sells its byproducts to chemical companies.