AQL (acceptance quality limit)

Inspecting every unit is often impractical, so buyers inspect a sample whose size depends on lot size and inspection level, following standards such as ISO 2859-1 or ANSI/ASQ Z1.4. If the defects found exceed the number allowed for the chosen AQL, the lot is rejected or sorted. Defects are classified as critical, major or minor, each with its own AQL; in consumer-goods inspection a common choice is zero tolerance for critical defects, 2.5 for major and 4.0 for minor.

AQL is an agreement between you and your factory or inspection agency, not a guarantee. A lot that passes can still contain defective units; the plan controls long-run average risk.

Where it bites: undefined defect classes ("what counts as a major scratch?") cause disputes. A defect list with photos and limits, plus golden samples, makes AQL meaningful.