What is a by-product?

A by-product is specifically defined as a leftover product that is generated during the manufacturing process or as a result of producing the main product. This means that while the primary focus of the manufacturing process is to create the main product, smaller quantities of other materials or substances may be produced unintentionally. These by-products can sometimes have value and can be repurposed, but they are not the primary focus of the production process.

In contrast to this, the other choices describe different concepts. The main product refers to the primary output of a manufacturing process and does not capture the idea of a by-product. A waste product implies something that has no utility, which might not be true for by-products, as they can often be used in other applications. Lastly, a product designed specifically for reuse does not align with the definition of a by-product, which arises as part of the production process rather than being intentionally created for a specific purpose.