A handguard on firearms is a guard attached to the front of a firearm

Firearm

A firearm is a weapon that launches one, or many, projectile at high velocity through confined burning of a propellant. This subsonic burning process is technically known as deflagration, as opposed to supersonic combustion known as a detonation. In older firearms, the propellant was typically...

 to grip the weapon from the front. It allows the user protection from the barrel, which may become very hot when firing. It also gives room for more attachments to the weapon itself, such as an M203 grenade launcher

M203 grenade launcher

The M203 is a single shot 40 mm grenade launcher designed to attach to a rifle. It uses the same rounds as the older M79 break-action grenade launcher, which utilize the High-Low Propulsion System to keep recoil forces low. Though versatile, and compatible with many rifle models, the M203 was...

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A handguard (also known as a hilt, crossguard or crosstree) is also a part of a sword or knife that is just above the handle. It protects the wielder's hands from an opponent's blade should it happen to slide down the blade.