Simply that there is some form of statute (formal law passed by a parliament) which outlaws an action. If a law saws "do not drive on the left" then driving on the left is "prohibited by law". It is, to be honest, a bit of a tautology!
It means an action prohibited by the law. It is something illegal.
Law
Not prohibited by Federal law, MAY be prohibited by state law, or limits placed on parole. Check with your local law enforcement.
Prohibited drugs are drugs that aren't allowed by law.
That funds and supporting documents are available, and goods or services have been received.
no
Goods prohibited by law or treaty from being imported or exported, Illegal traffic in contraband; smuggling.
Speeding
Illicit Trade
DoD forces are prohibited from performing law enforcement functions by federal law. Use of the DoD to enforce internal law and order requires declaration of martial law by the president.
A society in which marriage between classes is prohibited by law or custom is based on a caste system.
sports,dancing,theatre
prohibited by law or by official or accepted rules