From the article: Intel again noted that it had reached a sub-0.40 D0 defect density (def/cm^2) for 18A, a critical measurement of the yield rate for a process

From the article: Intel again noted that it had reached a sub-0.40 D0 defect density (def/cm^2) for 18A, a critical measurement of the yield rate for a process node. A process node is usually considered production-worthy and healthy once D0 reaches 0.5 or below.