by·prod·uct • n. (also by-prod·uct) an incidental or secondary product made in the manufacture or synthesis of something else: zinc is a byproduct of the glazing process. ∎  a secondary result, unintended but inevitably produced in doing or producing something else: he saw poverty as the byproduct of colonial prosperity.

by-product In mining, subsidiary material worked from ore deposits in which other materials are dominant. In some cases the revenue from the by-products can exceed that from the major type, e.g. gold from porphyry copper deposits. Compare CO-PRODUCT.