Scum/skʌm/ Definition 1 of 2Pro Tip 1/3Literal meaning Scum refers to actual physical dirt on liquids like water or soup. You'll need to skim the scum off the top of the boiling broth. Pro Tip 2/3Cleaning context Scum is often mentioned when discussing cleaning fish tanks, ponds, or cooking pots. After the fish tank was cleaned, there was no scum left. Pro Tip 3/3Negative perception When 'scum' refers to dirt, it suggests neglect or unclean conditions. The bathtub is filthy with soap scum.