known-good die
Beginner
A chip that has been fully tested before it is packed in with other chips.
Novice
A bare chip tested thoroughly while still on the wafer, before it is assembled with other chips, so it is very unlikely to make an expensive multi-chip package fail.
Expert
Wafer-level test coverage high enough to keep package-level yield acceptable. It pushes at-speed test and die-to-die interface test forward to wafer sort, where probing is harder than on a packaged part.
Explained in AI accelerators and datacenter (Industries).