noun

• (UK, Ireland, Australia, slang, derogatory) A prostitute or promiscuous woman; a slut.
  "1984, Tristan Jones, Heart of Oak, 1997, paperback edition, page 260, We never talked about that, of course; we talked about how we could find a woman in the Dilly, and if the Yanks had taken them all, how we could always resort to the peroxided older slags who hung out around the side doors to Waterloo station and did knee tremblers for the Yanks."
• (UK, Ireland, derogatory, dated) A coward.
• (UK, Ireland, chiefly Cockney, derogatory) A contemptible person, a scumbag.
  "The writers took it for granted that England, with its working class composed of slags, purple-nosed losers, and animals fed on pinball, pornography and junk-food, was disintegrating into terminal class-struggle."

verb

• (transitive) To produce slag.
• (intransitive) To become slag; to agglomerate when heated below the fusion point.
• (transitive) To reduce to slag.
• (transitive, UK, slang) To talk badly about; to malign or denigrate (someone).
  "If you slag off the other person, then—to the extent that your child identifies with that person as their parent—you are slagging off a part of them."