This is a question about Damage Reduction, not Damage Resistance (which is not supposed to work properly anyway).
If I have a damage reduction of 5/, what damage am I reducing by 5 points?
Physical Damage - (Slashing, Bludgeoning, Piercing)?
Elemental Damage - (Fire, Cold, Electric, Acid, Sonic)?
Energy Damage - (Positive energy, Negative energy)?
Magic Damage - (Good, Evil, Chaotic, Lawful, Beasts, All)?
Some other damage I have not listed?
Some combination of these? All of them?