What is the difference between 'Joint products' and 'by-product' and explain how they for accounted for in process costing?

Joint products are two or more product produced from the same process both having high saleable value while by products are the one which are produced incidentally and may have or have not some value.

The pre separation cost is apportioned between the joint product on some basis like sale value, units of production, and for by products their value is deducted from the separation cost.