The term 'Smelter's Waste' is often used to refer to the by-product of smelting, which is a process used to extract metals from ore. The crossword solution for this term is SLAG, which is a type of waste material that is created during the smelting process. It is usually composed of a mixture of metal oxides and other impurities. SLAG is typically discarded as waste, but can also be used in construction materials or as a fertilizer.