Out of bounds.
Out of bounds.
The expression 'out of bounds' originally comes from sports, where it refers to areas outside the play area where the ball is not permitted. By extension, this phrase now also metaphorically means an area or subject matter that is off-limits or forbidden. This could refer to physical locations you're not allowed to enter or topics that are considered inappropriate to discuss in certain social contexts. For instance, asking about someone's salary in a casual conversation is often considered 'out of bounds.'
Going beyond the fence is out of bounds.
Going beyond the fence is forbidden.
The restricted area is out of bounds for visitors.
The restricted area is off-limits for visitors.
Cheating on the exam is definitely out of bounds.
Cheating on the exam is completely unacceptable.