"According to our convention ‘decriminalisation’ comprises removal of a conduct or activity from the sphere of criminal law. Prohibition remains the rule, but sanctions for use (and its preparatory acts) no longer fall within the framework of the criminal law (elimination of the notion of a criminal offence). This may be reflected either by the imposition of sanctions of a different kind (administrative sanctions without the establishment of a police record – even if certain administrative measures are included in the police record in some countries, such as France), or the abolition of all sanctions. Other (non-criminal) laws can then regulate the conduct or activity that has been decriminalised.
"According to our convention ‘depenalisation’ means relaxation of the penal sanction provided for by law. In the case of drugs, and cannabis in particular, depenalisation generally signifies the elimination of custodial penalties. Prohibition remains the rule, but imprisonment is no longer provided for, even if other penal sanctions may be retained (fines, establishment of a police record, or other penal sanctions)."

Source

European Monitoring Center on Drugs and Drug Addiction, "Illicit drug use in the EU: legislative approaches" (Lisbon, Portugal: EMCDDA, 2005), p. 12,
http://eldd.emcdda.europa.eu/…