Meaning of SLAG in English
I. slag 1 /slæɡ/ BrE AmE noun
[ Date: 1500-1600 ; Language: Middle Low German ; Origin: slagge ]
1 . [countable] British English taboo informal a very offensive word for a woman who has sex with a lot of different people. Do not use this word.
2 . [uncountable] a waste material similar to glass, which remains after metal has been obtained from rock
II. slag 2 BrE AmE verb ( past tense and past participle slagged , present participle slagging )
slag somebody ↔ off phrasal verb British English informal
to criticize someone in an unpleasant way, especially when this is unfair:
He’s always slagging her off behind her back.
Longman Dictionary of Contemporary English. Longman - Словарь современного английского языка. 2012