In Dominions, Resistance refers to a trait that provides damage reduction against a particular type of damage.
Elemental Resistances are point value traits, such as "Fire Resistance (5)". They function by reducing the impact of elemental attacks, directly lowering their strength/power before the Damage Roll. New to Dominions 6, they then reduce damage like the Physical Resistances, at a rate of 2% per point. Elemental Vulnerabilities exist, too; think of them as "negative" Resistances.
Magic Resistance is technically not a Resistance stat, though it provides protection against a wide array of effects. Think of it like Defence Skill (or Armor Class) for certain not-physical, not-elemental things.