Radiant Void Staff

radiant

Attacks and Ability damage 30% Shred the target for the rest of combat. This effect does not stack.

Shred: Reduce Magic Resist

Source

Shred

Shred is a debuff that reduces the target's Magic Resist.
Mana

Mana is the unit-level resource that gates ability casts.
Mana Regen

Mana Regen is a stat that trickles Mana into a unit every second on its own.
Ability Power

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

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

On Hit is an effect that fires on each basic attack that lands.

Magic Resist

Magic Resist is the magic-defense stat that reduces incoming Ability Power (AP) damage.