The entry indicates the amount of damage ignored (usually 5 to 15 points) and the type of weapon that negates the ability.
Some monsters are vulnerable to piercing, bludgeoning, or slashing damage.
Some monsters are vulnerable to certain materials, such as alchemical silver, adamantine, or cold iron. Attacks from weapons that are not made of the correct material have their damage reduced, even if the weapon has an enhancement bonus.
Some monsters are vulnerable to magic weapons. ... Such creatures’ natural weapons ... are treated as magic weapons for the purpose of overcoming damage reduction.
A few very powerful monsters are vulnerable only to epic weapons.... Such creatures’ natural weapons are also treated as epic weapons for the purpose of overcoming damage reduction.
Some monsters are vulnerable to chaotic-, evil-, good-, or lawful-aligned weapons. ... A creature with an alignment subtype (chaotic, evil, good, or lawful) can overcome this type of damage reduction with its natural weapons and weapons it wields as if the weapons or natural weapons had an alignment (or alignments) that match the subtype(s) of the creature.
