Waste matter is a broad term that can refer to a variety of materials, including GARBAGE, DROSS, RUBBISH, SCUM, LITTER, DREGS, and SEWAGE. GARBAGE is a common term for waste matter that is discarded as no longer useful or wanted. DROSS is a term for impurities or waste matter that is removed from a molten metal during the smelting process. RUBBISH is a British term for waste matter that is thrown away as no longer useful or wanted. SCUM is a term for a thin layer of waste matter that forms on the surface of a liquid. LITTER is a term for waste matter that is left in an outdoor area, such as a park or beach. DREGS are the sediment or residue of a liquid, such as the bottom of a cup of coffee. SEWAGE is a term for waste matter that is carried away in sewers, such as human waste and wastewater.