Possession of a prohibited firearm is defined as the possession or control of a firearm that is prohibited by Canadian law, without being authorized to do so. This can include certain types of firearms, such as fully automatic weapons or handguns with a barrel length of less than 105 millimeters. Possession of a prohibited firearm can carry a significant penalty, including a prison sentence of up to 10 years. Additionally, the penalties for possession of a prohibited firearm can be increased if the firearm is used in the commission of another criminal offense, such as armed robbery or assault.