14 C.F.R. § 251.1
As used in this part:
Certificated air carrier means a U.S. carrier holding a certificate issued under 49 U.S.C. 41102 to conduct passenger service or holding an exemption to conduct passenger operations under 49 U.S.C. 40109 .
Commuter air carrier means a U.S. carrier that has been found fit under 49 U.S.C. 41738 and is authorized to carry passengers on at least five round trips per week on at least one route between two or more points according to a published flight schedule using small aircraft as defined in 14 CFR 298.2 .
Covered carrier means a certificated carrier, a commuter carrier, an air taxi, or a U.S. indirect carrier operating to, from, or within the United States, conducting scheduled passenger service or public charter service.
Indirect carrier means a person not directly involved in the operation of an aircraft who sells air transportation services to the general public other than as an authorized agent of a carrier.
14 C.F.R. §251.1