1. Any previous health insurance coverage that can be used to shorten the preexisting condition waiting period. See also preexisting condition. 2. Under a Medicare Part D plan, a prescription drug coverage from another private insurance plan (Medigap and employer plans) that meets certain Medicare standards. When a patient is enrolled in a drug plan that gives prescription drug coverage, the plan tells the patient that coverage is equal to or better than the standard model and it is considered creditable coverage. Also called creditable prescription drug coverage.