AQL- Acceptable Quality Limit is a standard for determining product defect ratio. Generally, because of large product quantity, we can't inspection all the products (except for full inspection), only can inspect a random sample products. And through the sampling products to determine all the quality of the products; So we can only through calculating the percentage of defective products in samples to know that all the products defect ratio.

Normally AQL numbers smaller mean standards more strict. That is to say, the lower the proportion of defective products.