AOCV (advanced on-chip variation)
Beginner
A safety margin that shrinks on paths with more steps, because small random errors tend to cancel out.
Novice
A way of setting timing safety margins that depends on the path: long chains of gates get a smaller margin per gate, because random differences between gates partly cancel out, and paths spread far across the chip get a larger one.
Expert
Derates looked up from tables by path depth (number of stages) and distance, instead of one flat percentage. Depth models random variation, which averages out over many stages; distance models systematic variation across the die. At advanced nodes it has largely given way to POCV with LVF.