Coal residue is the material left over after coal has been burned. EMBER, COKE, CINDER, and SLAG are all forms of coal residue. EMBER is a glowing, red-hot fragment of wood or coal that is left after a fire has burned out. COKE is a solid carbonaceous material derived from destructive distillation of low-ash, low-sulfur bituminous coal. CINDER is a light, porous form of coal residue created by incomplete combustion of coal. SLAG is a glassy, granular material formed when molten ash from coal is cooled.