If you ever played Diablo 2, you can compare it to Enhanced Damage. It basically increases the effect of whatever item it is on.
If it's on a weapon, it makes the weapon do more damage.
If it's on an armor, it makes the armor have more defense.
If it's on a damage charm, it makes the damage charm do more damage.
If it's on a heal charm, it makes the heal charm heal for a higher amount.