the united states department of homeland security defines a personal defense weapon as an m4 carbine (or a colt ar-15 civilian semi-automatic rifle). some governments' definition of pdws includes handguns. an example is the czech republic. it has proposed a constitutional amendment which would allow its citizens to own and keep pdws as a way to discourage terrorists. regardless, a pdw is usually agreed upon as being somewhere between a submachine gun and an assault rifle.