AQL - Acceptable Quality Level

       
The AQL of a sampling plan is a level of quality routinely accepted by the sampling plan. It is generally defined as the percent defective (defectives per hundred units X 100%) that the sampling plan will accept 95% of the time. This means lots at or better than the AQL are accepted at least 95% of the time and rejected at most 5% of the time. 

The AQL can be determined using the operating characteristic (OC) curve by finding that quality level on the bottom axis that corresponds to a probability of acceptance of 0.95 (95%) on the left axis.
  
Associated with the AQL is a confidence statement one can make. If the lot passes the sampling plan, one can state with 95% confidence that the quality level of the lot is equal to or better than the AQL (i.e., the defective rate of the lot < AQL). On the other hand, if the lot fails the sampling plan, one can state with 95% confidence that the quality level of the lot is worse than the AQL. 
  
The AQL describes what the sampling plan will accept, but it is also important to know what the sampling plan will reject. Information on what the sampling plan will reject is provided by the LTPD of the sampling plan.

Table 2. AQL Sampling Table based on the Mil-STD-105D