Redundant (double) via
Beginner
Using two vias side by side instead of one, so the connection still works if one is badly made.
Novice
Replacing single-cut vias with two or more cuts side by side wherever space allows, usually in a pass after detailed routing. If one cut fails to form in manufacturing, the other still connects, and two cuts in parallel also resist current less.
Expert
A post-route optimization that tries alternative via shapes at each location without creating new rule violations, tracked as a double-via rate. Some rules require several cuts on wide wires (LEF MINCUTS in non-default rules). Via pillars are a structured relative.