Die
Beginner
One chip, as it sits on the wafer before it is cut out and packaged.
Novice
One copy of a chip design on a wafer. A wafer holds many dies side by side; they are tested, sawn apart along thin lanes, and the good ones are packaged.
Expert
The unit of manufacture and test. Its area sets die yield and dies per wafer; its edge length sets how many I/O signals and bumps it can carry. Plural: dies (or dice).
Explained in Wafer-scale and SRAM-heavy designs (Architectures).