Some warriors have honed the craft of killing into an art. Tales are told of master swordsmen who can decapitate a man with one stroke of their blade.
If a model with the killing blow special rule rolls a 6 when rolling to wound in close combat, he automatically slays his opponent. Noor saves are allowed against this wound, though can be taken as normal.
This attack is only effective against models with a unit strength of 2 or less. It can be used against characters mounted on chariots and characters mounted on monsters, as long as the riders themselves have a unit strength of 2 or less and only hits directed against the rider and not the mount/chariot will use the killing blow rule.
Rarely some models may have the ability of using the killing blow rule with ranged attacks (such as spells or missile weapons). When this is the case, it will be clearly specified in their special rules in the relevant Army book's entry.