42 C.F.R. § 411.21
In this subpart B and in subparts C through H of this part, unless the context indicates otherwise-
Conditional payment means a Medicare payment for services for which another payer is responsible, made either on the bases set forth in subparts C through H of this part, or because the intermediary or carrier did not know that the other coverage existed.
Coverage or covered services, when used in connection with primary payments, means services for which a primary payer would pay if a proper claim were filed.
Monthly capitation payment means a comprehensive monthly payment that covers all physician services associated with the continuing medical management of a maintenance dialysis patient who dialyses at home or as an outpatient in an approved ESRD facility.
Plan means any arrangement, oral or written, by one or more entities, to provide health benefits or medical care or assume legal liability for injury or illness.
Primary payer means, when used in the context in which Medicare is the secondary payer, any entity that is or was required or responsible to make payment with respect to an item or service (or any portion thereof) under a primary plan. These entities include, but are not limited to, insurers or self-insurers, third party administrators, and all employers that sponsor or contribute to group health plans or large group health plans.
Primary payment means, when used in the context in which Medicare is the secondary payer, payment by a primary payer for services that are also covered under Medicare.
Primary plan means, when used in the context in which Medicare is the secondary payer, a group health plan or large group health plan, a workers' compensation law or plan, an automobile or liability insurance policy or plan (including a self-insured plan), or no-fault insurance.
Prompt or promptly, when used in connection with primary payments, except as provided in § 411.50 , for payments by liability insurers, means payment within 120 days after receipt of the claim.
Proper claim means a claim that is filed timely and meets all other claim filing requirements specified by the plan, program, or insurer.
Secondary, when used to characterize Medicare benefits, means that those benefits are payable only to the extent that payment has not been made and cannot reasonably be expected to be made under other coverage that is primary to Medicare.
Secondary payments means payments made for Medicare covered services or portions of services that are not payable under other coverage that is primary to Medicare.
42 C.F.R. §411.21