An anti-personnel weapon is one primarily used to incapacitate people, as opposed to attacking structures or vehicles. Anti-personnel weapons were made and used since the discovery of weapons for hunting.
The development of defensive fortification and combat vehicles gave rise to weapons designed specifically to attack them, and thus a need to distinguish between those systems and ones intended to attack people. For instance, an anti-personnel landmine will explode into small and sharp splinters that tear flesh but have little effect on metal surfaces, while anti-tank mines have considerably different design, using much more explosive to effect damage to armored fighting vehicles.
Many modern weapons systems can be employed in different roles, for example a tank's main gun can fire armor-piercing ammunition in the anti-tank role, high-explosive ammunition in the anti-structure role and fragmentation shells in the anti-personnel role.
There are also more exotic classes of weapons, such as neutron bombs, chemicals, and biological weapons which are only designed to attack people. As there is greater international criticism of them, they are therefore rarely 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. Such weapons often create much collateral damage and may affect large numbers of civilians.