the extraneous matter or impurities which rise to the surface of liquids in boiling or fermentation, or which form on the surface by other means; also, the scoria of metals in a molten state; dross.-refuse; recrement; anything vile or worthless.-to take the scum from; to clear off the impure matter from the surface of; to skim.-to sweep or range over the surface of.-to form a scum; to become covered with scum. also used figuratively.