also: わるくち
noun
abuse; slander; bad-mouthing; insulting remarks
Refers to speaking ill of someone, often behind their back. Common in phrases like 悪口を言う.
彼はいつも人の悪口を言っている。
He is always bad-mouthing people.
陰で悪口を言う
It's not good to speak ill of others behind their backs.