Radiant Edge of Night

radiant

At 40% Health, briefly become untargetable, shed negative effects, and heal all missing health.

Source

Heal

A Heal restores Health to a unit.
Untargetable

Untargetable is a protective state where the unit stops being a valid target.
Armor

Armor is the physical-defense stat that reduces incoming Attack Damage (AD) damage.
Ability Power

Ability Power (AP) scaling means an effect gets stronger when its holder stacks AP.
Attack Damage

Attack Damage (AD) scaling means an effect gets stronger when its holder stacks AD.
Attack Speed

Bonus Attack Speed (AS) makes a unit attack more often per second.

Missing Health Scaling

Missing Health is the gap between a unit's max Health and the Health it has left.