Translation guide
The act of speaking negatively about someone who is not present, often in a malicious or unfair way.
She often backbites about her colleagues.
Stop backbiting.
Literally 'to say bad things in the shadows'. A more explicit alternative to 陰口を叩く.
He is always backbiting about people behind their backs.
Noun meaning 'backbiting' or 'malicious gossip'. Often used with を言う or を叩く.
There is a lot of backbiting in that group.
General term for 'badmouthing' or 'speaking ill of someone'. Not necessarily behind their back, but often used in that context.
It's rude to speak ill of him.
Formal term for 'slander' or 'defamation', often used in legal or serious contexts. Stronger than casual backbiting.
Online slander has become a problem.
To refer to the behavior itself as a noun.
Do not translate 'backbiting' literally as 背中噛み (back biting). This makes no sense in Japanese. Use the idiomatic expressions above.
陰口 (kageguchi) specifically means speaking ill of someone behind their back, while 悪口 (waruguchi) is more general badmouthing that can be done to someone's face or behind their back. For 'backbiting', 陰口 is more precise.
She never stops backbiting behind the scenes.