Submachine Gun: Pistol caliber, fully automatic, and fitted with a shoulder stock. For example, Thompson, MP40, MAS-38.
Machine pistol: Handgun form factor and fully automatic. For example, Glock 18, Mauser Schnellfeuer, Stechkin.
Automatic Rifle: Shoulder or hip fired, limited magazine capacity, minimal sustained fire capacity. Examples: M1918 BAR, Chauchat.
Persinal Defense Weapon: (1) Armor-piercing or (2) holsterable submachine gun, not intended for front line combat. For example, FN P90, H&K MP7, Czech vz.61 Skorpion, Polish PM63 Rak.