Void Damage
Void damage ignores the matchup entirely, so every hit lands at its base value whatever the foe is weak to or resists. While the Ginnungagap Shard's Void window is open, everything you deal turns Void — chains, splash, Ability bolts, status ticks, charm procs alike. You stop losing damage to resistances, and you give up your weakness bonus for the same window.
In detail
While the Void window is open, weakness and resistance multipliers are forced to 1.0, so every hit lands at its base value. Chain damage and Lightning Rod ticks are the two paths this changes. Chain Lightning's bolt, splash and burn ticks ignore the matchup at all times already, so the window simply brings everything else in line with them.
More in glossary
From the current development build. Content and balance may change before release. This public reference includes discoveries and does not reflect your personal unlocks.