Everything is called a weapon system.
I hate that, some douche on the military channel called a spear a weapon system. If I was there when he said that I'd have punched him in the face.
/agree, "weapon system" is a completely meaningless thing to say, it's just an example of stupid people playing with 'long' words to sound technical.
A gun is any weapon that propels a projectile by combustion. Everything from a cannon to a flint-lock pistol is a gun.
A weapon is any tool, object or device that can be utilized to inflict injuries to any living thing.