taboo word; forbidden topic
A word or topic that is socially or contextually off-limits; common in everyday conversation.
Talking about divorce is a taboo topic in front of him.
In this meeting, salary talk is a forbidden topic.
forbidden words (in classical poetry)
Original meaning: words or phrases prohibited in traditional waka and haikai poetry. Now a historical/literary term.
In waka, words like 'tears' and 'death' were sometimes considered forbidden.
The topic of divorce is off-limits in front of him.
At this company, talk of salaries is treated as a forbidden topic.
Bringing up her age is a no-go with her.