Also known as “donut hole.” Coverage gap in Medicare Part D prescription drug coverage, as originally enacted, where enrolled beneficiaries paid 100 percent of their prescription drug costs after their total drug spending exceeded an initial coverage limit until they qualified for catastrophic coverage. Beginning January 1, 2011, the Affordable Care Act (ACA) began shrinking the doughnut hole by reducing beneficiary copayments each year, until the doughnut hole is essentially eliminated by 2020. (See Medicare chapter.)