not allowed, especially because of an official rule [↪ banned]
it is forbidden (to do something)
It is forbidden to smoke at school.
be strictly/expressly/absolutely etc forbidden
Alcohol is strictly forbidden in Saudi Arabia.
a forbidden place is one that you are not allowed to go to
The Great Mosque is forbidden to Christians.
a forbidden activity, subject etc is one that people think that you should not do, talk about etc:
Sex was always a forbidden topic.
forbidden fruit (=something that you should not have, but that you want)
Forbidden fruit is always more attractive.