Process-voltage-temperature (PVT)
PVT names the three knobs that make two physically identical chips run at different speeds: how the silicon happened to come out of the fab (Process), what supply it's powered at (Voltage), and how hot it is (Temperature). No two transistors are truly identical — random fabrication spread means some wafers turn out 'fast' and others 'slow'. A higher supply voltage gives transistors more drive and speeds them up; temperature is sneakier, generally slowing gates when hot but, at low voltages, sometimes doing the reverse (temperature inversion).
STA can't analyze the infinite continuum of real conditions, so the foundry boils it down to discrete PVT corners — labeled like SS (slow-slow), FF (fast-fast), TT (typical) — each a worst-case bundle of the three. The slow corner stresses setup; the fast corner stresses hold; and a robust chip must pass at both extremes, because over its life it will be cold and warm, fresh-batteried and drained, lucky-die and unlucky-die. PVT is the raw material that the corner list in MCMM is built from.
Two opposite corners must both pass for a robust chip.
Modern advanced nodes often add aging and self-heating as extra dimensions — a transistor literally gets slower over years of use, so signoff increasingly checks an 'end-of-life' PVT that the chip won't even hit until it's old.