Meaning of “scum” - Learner’s Dictionary

scum

noun uk us /skʌm/
SUBSTANCE [ U, no plural ]

an unpleasant, thick substance on the surface of a liquid:

There was a thick layer of scum on the water.
PERSON [ U ] informal

an offensive way of referring to a very bad person

(Definition of “scum” from the Cambridge Learner’s Dictionary © Cambridge University Press)