by-product
noun [ C ]
uk/ˈbaɪˌprɒdʌkt/ us PRODUCTION
something that is produced as a result of making something else:
a by-product of sth Selenium is a by-product of copper refining.
oil/animal/chemical by-products
something not expected or not intended that happens as a result of something else:
a by-product of sth Higher than expected tax revenues were a by-product of the booming economy.