be off limitsa) if a place is off limits, you are not allowed to go there 禁止入内 SYN out of boundsbe off limits to/for Footpaths are, of course, off limits to bikers. 人行道当然不允许骑车。
b) if a subject is off limits, you are not allowed to talk about it 禁止谈论 Unlike most group discussions, nothing was off limits. 话题没有限制,这和大多数小组讨论不一样。
→ be off limits at off limits(1)