I believe he means counter abilities such as (and correct me if you haven't played Final Fantasy Tactics Gubid) hamedo, weapon guard, counter tackle, etc. Basically an ability that allows you to counter attack an enemy when attacked. Such as:
Enemy targets your character -> Your character has a 65% chance of performing a counter attack (percentage based on level, or maybe DEX) -> if attack proceeds, enemy is hit, if not, then no counter-damage is inflicted
Basically, a skill could be placed in the database and added into the script somehow as a counter attack that is activated whenever the enemy attacks and takes into account the hit rate of the skill. How you would add in something like hamedo (attack before being attacked), I have no idea.