Slag is a byproduct formed during the smelting process of metals, particularly in the extraction of iron and copper. It consists of various impurities, such as silica, alumina, and iron oxides, that are separated from the desired metal. When ore is heated, these impurities melt and rise to the surface, where they can be removed. In addition to its role in metallurgy, slag can be repurposed in construction and road building. It is often used as an aggregate in concrete or as a base material for roads, providing a sustainable option for recycling industrial waste.