Definition & Meaning of "scum"in English

What is the origin of the term "scum" and how is it used?

"Scum" comes from a Middle English word referring to the layer of dirt or foam that forms on the surface of liquids, especially during boiling or decay. By metaphor, it was applied to people by the 19th century to suggest moral filth or worthlessness. It is used in insults, crime reporting, or heated arguments to label someone as despicable or contemptible. The term is strongly derogatory but not necessarily vulgar.