• A layer of impurities that accumulates at the surface of a liquid (especially water or molten metal)
• A greenish water vegetation (such as algae), usually found floating on the surface of ponds
• The topmost liquid layer of a cesspool or septic tank
• English Slang, derogative term meaning worthless person or persons (with the above meanings in mind), hence scumbag or scumbucket.

The name scum is also used for:

• Scum (album), a 1987 album by grindcore band Napalm Death
• Scum (band) - Norwegian/American punk/metal band
• Scum (film), a 1977 television play directed by Alan Clarke, and the 1979 cinematic version
• SCUM Manifesto (Society for Cutting Up Men), a 1968 radical feminist book by Valerie Solanas
• "Scum" (single), song by the band Meat Puppets
• SCUMM (Script Creation Utility for Maniac Mansion), scripting language developed at LucasArts to ease development of the graphical adventure game Maniac Mansion

Scum may also refer to:

• Scum, one of many names for the card game President
• Scum, former name of the melodic death metal band Amon Amarth
• SCUM, the New Wave, Gothic band featuring Huw Webb, Rhys Webb's [Spider of the Horrors] brother