42 CFR §401.303

For purposes of this subpart— Medicare contractor means a Part A/Part B Medicare Administrative Contractor (A/B MAC) or a Durable Medical Equipment Medicare Administrative Contractor (DME MAC). Overpayment means any funds that a person has received or retained under title XVIII of the Act to which the person, after applicable reconciliation, is not entitled under such title. Person means a provider (as defined in § 400.202 of this chapter) or a supplier (as defined in § 400.202 of this chapter).