ETYM Swed. slagg, or lg. slacke, whence German schlacke; originally, perhaps, the splinters struck off from the metal by hammering. Related to Slay.
The dross or scoria of a metal.
In chemistry, the molten mass of impurities that is produced in the smelting or refining of metals.
The slag produced in the manufacture of iron in a blast furnace floats on the surface above the molten iron. It contains mostly silicates, phosphates, and sulfates of calcium. When cooled, the solid is broken up and used as a core material in the foundations of roads and buildings.
The scum formed by oxidation at the surface of molten metals; SYN. scoria, dross.

(chiefly British) To criticize harshly

(chiefly British) A lewd or promiscuous woman