A dependent product is a product output from an activity whose production volume depends on demand for other products from the same activity rather than on direct market demand for the dependent product itself. This term is synonymous with By-product.
The terminology emphasises the dependent nature of these products in multi-output activities. Whilst an activity may produce several product outputs simultaneously, only some of these products determine the production volume of the activity. The dependent products are produced as a consequence of producing the determining products, rather than being the primary reason for conducting the activity.
In the context of Life Cycle Assessment modelling, understanding whether a product is dependent or determining is essential for proper system boundary definition and for applying appropriate modelling approaches such as system expansion or allocation. The classification affects how environmental burdens are attributed and how substitution effects are accounted for in consequential LCA.
