An anti-personnel weapon is one primarily used to injure or kill people. Because these do not discriminate between soldiers and civilians, there are international political movements to ban these various weapons. The most common use of this term is for certain low-powered explosive devices.
While the distinction is very old—a spear is anti-personnel, while a catapult is of more use against buildings than individuals—the large-scale development of military technology in the 19th and 20th centuries has made the concept a key consideration in design. For instance, an anti-personnel landmine will explode into small and sharp splinters that tear flesh but have no effect on metal surfaces, and will be designed not to explode when a vehicle rolls over it.
The most common modern anti-personnel weapons are cluster bombs, claymore mines, and booby traps. A hand grenade is generally used as an anti-personnel weapon, though it can destroy light vehicles and structures, but it isn't generally referred to as one because it is hurled at a specific, tactical target and its results are immediate, rather than randomly sown to deny access to a stretch of ground and left around until it detonates.
There are also more exotic classes of weapons, such as neutron bombs, chemicals, and biological weapons which only attack people. But as there is greater international criticism of them, they are therefore not used. These are not generally referred to as anti-personnel weapons, but by their own names or group terms (e.g., NBC weapons) which serve to get them specifically banned.
The original article can be found at Anti-personnel weapon and the edit history here.