PVT corner
Beginner
One extreme case the chip must still work in, such as a slow chip on a hot day.
Novice
One combination of process (whether the factory made the transistors slow, typical or fast), supply voltage and temperature. Each corner has its own timing data for the building blocks. Signals are usually slowest at slow process and low voltage, and fastest at fast process and high voltage.
Expert
Named by the speed of the NMOS and PMOS transistors (slow-slow, typical, fast-fast, and the skewed slow-fast and fast-slow), with a voltage and temperature, each with its own Liberty library. Every independent supply multiplies the set. At low supply voltages some processes get slower when cold, not hot, so teams check both temperatures at the slow corner.
Explained in Signoff (Design Flow).
See also: RC corner, MCMM (multi-mode multi-corner).