Slaying
Slaying is an attack property that can be found on some magic weapons that can “slay” various races of creatures. When you examine a weapon, if it says something like (Slay Dragon) or (Slay Demon) it has a slaying property for the listed race(s). If the weapon slays the defender, the attack damage is tripled, making it very powerful against those specific enemy types.
It's also possible to add slaying to a weapon by worshipping a god, having a high level of Praying, and having your god bless your wielded weapon which, depending on the weapon's existing properties, can add slaying or new attack types.
Slaying cannot appear on any equipment other than wieldable weapons and bow/crossbow ammunition. In theory, this is one of the reasons that Dragons, Fireborn, and any other races that choose to be Monks or Gaea followers will never be top tier physical attackers as characters that can't wield weapons have no way to swap weapons to benefit from slaying properties on specific monsters. And being able to triple your damage by swapping to a slaying weapon is a huge advantage against dangerous and durable monsters!
However, some high level boss monsters actually have their race manually overridden from what they're normally considered to be, specifically to make them immune to slaying and thus much more resistant to your physical attacks than what you'd expect. Boss monsters like this also end up being immune to Banishment spells from the followers of gods that would normally target that particular race. Monster race, which determines if it's susceptible to a slaying type, is typically defined by the race listed in a monster's arch configuration file. Map makers can be manually change it for unique monsters to be something entirely different, such as making a high level dragon with unique resistance values and much higher than normal HP, and a race set to something like “Divine” to make it immune to slaying from something like a Dragonslayer.