This is not a trick question, nor a play on words. It is a fundamental way of posing a question that needs a full answer - before any criminology student proceeds to the second level of their studies or before any criminology worth its salt can be considered scientific.
Here are some outline answers, which of course warrant much further discussion:
1 When it is an action or practice which most people see as criminal but which is not technically an infringment of the criminal law.
2 When the action or practice is technically an infringement of the criminal law, and is popularly seen as criminal, but which is hardly ever prosecuted as such by the authorities.
3 When the action or practice is technically an infringement of the criminal law, and is not widely seen as criminal, and is hardly ever prosecuted as such because of that.
4 When it is an action or practice that is a crime in one jurisdiction but actually carried out in another jurisdiction, e.g. another country, that does not prosecute that crime or even recognize it as a crime within its own criminal law.]]>