It means something you must not do. But the words "must not" bear no tangible or concerete meaning. So I think forbidden means any action that if done, will be faced with punishment.
  But does  "punishment" only mean depriving someone of life, amputating his limbs etc. ?
  Can we say that denying a man his other needs, because of he has done, too is a form of punishment, meaning that his action were sth forbidden?

  For example: if someone tells you that something is allowed simply because they wont kill or imprison you as a result of it, will you be persuaded of it's lawfulness?
  If an action is met with loss of honor, affection, comunication etc. to me it means that that action was kinda taboo, illegal or simply "not allowed." (though there is different degrees of badness between what ends in capital puishment and what ends in isolation for sure.)

  Any ideas?
 

Forbidden is like condemned!

To be forbidden means that there is a law, a Divine Law or a human law, that it must not be done.

However, forbidden might mean, that something impossible.  That is, it is prevented by "laws" that the rules of existence must follow.

Forbidden and bad do not mean the same things in human terms, but in terms of religion it is clear that anything that is a matter of our choice - is forbidden by God if it is bad.  Everything that God forbids has punishment attached.