What is crime? What might be legal today could be criminalised tomorrow. What is legal in one country can be punishable in another one. For example, up to the second half ot the 20th century, the trade and use of methamphetamine and its derivates (pervitin, crystal meth) was legal in the Western World. In the meantime it became illegal and processing, buying or dealing in these substances is punishable by law.
The definition is somewhat pragmatic: crime is what people understand it to be, especially determined by the outcomes of criminal jurisdiction.
It is a classification structure of criminal offences, published by the United Nations Office on Drugs and Crime (UNODC). On the basis of internationally agreed concepts and principles, the ICCS consists of a framework to assign criminal offences to hierarchical categories that have a certain degree of similarity in relation to conceptual, analytical and policy areas. The purpose of the ICCS is to enhance consistency and international comparability of crime statistics and improve analytical capabilities at both, the national and international levels. pdf
INTERNATIONAL CLASSIFICATION OF CRIME FOR STATISTICAL PURPOSES, United Nations Office on Drugs and Crime (UNODC) 2015