The highest/worst possible average percent of non-conforming items in the process, after employing some inspection scheme. This measure is usually used in rectifying inspection, where the inspection procedure changes the outgoing rate of non-conforming items in the batch or process, relative to the incoming rate. For example, by removing the non-conforming items that are encountered during inspection. Note that this is only the worse possible average percent of non-conforming items, and therefore there is still a possibility that the percent non-conforming of a single batch will exceed this limit.
It is not enough to do your best; you must know what to do, and then do your best.