Qualification is the formal evidence package that a part will keep working for its intended lifetime, in its intended environment. That's a distinct question from functional verification ("does the design work as specified") and from production test ("does this specific unit work right now"). A part can pass both of those and still fail qualification if it can't survive years of thermal cycling or electrostatic events in the field.
The industry leans heavily on standards published by bodies like JEDEC to make qualification results comparable across companies. Common test families include HTOL (High-Temperature Operating Life: running parts under elevated temperature and voltage for an extended duration to accelerate wear-out failure modes), temperature cycling (repeatedly cycling between hot and cold extremes to stress package and interconnect integrity), HAST or autoclave testing (humidity and pressure, screening for moisture-related failures), ESD testing (human-body-model and charged-device-model discharge, screening for electrostatic damage tolerance), and latch-up testing (checking the part doesn't enter a destructive high-current state under transient disturbance).
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