An item which is used to a manner involving confrontation to make someones life unpleasant. This sort of unpleasantness will invariably be painful and possibly fatal. They can make you feel very ally, but remember that real people give a good old slapping.
Weapons can be custom built for the job of inflicting unpleasantness (a firearm) or can be a normal everyday item pressed into emergency use for the spreading of pain (brick, kitchen knife, pub ashtray). The armed forces of a country will make use of the custom weapons while a country's neds and chavs are specialists in the use of the ad hoc ones.
The range at which a weapon functions can vary from extremely close (teeth to nose distance), though arms length (sword) all the way up to intercontinental and even low earth orbit (reserved for future US expansion).
Historically weapons had short ranges with 300 yards being about the longest possible engagement range (longbow and early cannon). This upper limit remained inviolate up till the late 1700's when the area of unpleasantness started to expanded dramatically (artillery, rifled longarms and armed aircraft).
Also as time passed the numbers who could experience the unpleasantness within a limited time frame increased dramatically. At one time you were guaranteed personal service but after the 1800's, industrial methods of unpleasantness were much in demand (machineguns).