AP lost for the target

is a weapon effect that has a chance of reducing the AP from the attacked target.
Note: To be sure if the weapon really reduces AP from the target and not from your character, check the colour of the -AP, if it's red then it will reduce your ap, if it's black/green then it will reduce the target's AP.
Weapons that drain AP from the target are listed in :Category:AP Reduction weapons, or in this list:
<DynamicPageList>
category=AP Reduction weapons
allowcachedresults=true
</DynamicPageList>
Equipment that actually reduces the AP of the wielder are listed in :Category:AP penalty equipment, or in this list:
<DynamicPageList>
category=AP penalty equipment
allowcachedresults=true
</DynamicPageList>
Category:Game information