Joint products are two or more products manufactured simultaneously through the same process. The common manufacturing costs are called joint costs. Each product has a significant market value. Example - Gasoline and Kerosene are joint products of crude oil refining.
On the other hand, a by-product has significantly lower sales value compared to the firm's main manufactured product. Therefore, it does not affect the decision to produce. Example - saw dust from lumber mills, bone from meat packing etc.