14 CFR § 259.3 - Definitions.
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. 41102.
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, or a foreign air carrier operating to, from or within the United States, conducting scheduled passenger service or public charter service with at least one aircraft having a designed seating capacity of 30 or more seats.
Foreign air carrier means a carrier that is not a citizen of the United States as defined in 49 U.S.C. 40102(a) that holds a foreign air carrier permit issued under 49 U.S.C. 41302 or an exemption issued under 49 U.S.C. 40109 authorizing direct foreign air transportation.
Large hub airport means an airport that accounts for at least 1.00 percent of the total enplanements in the United States.
Medium hub airport means an airport accounting for at least 0.25 percent but less than 1.00 percent of the total enplanements in the United States.
Non-hub airport means an airport with 10,000 or more annual enplanements but less than 0.05 percent of the country's annual passenger boardings.
Small hub airport means an airport accounting for at least 0.05 percent but less than 0.25 percent of the total enplanements in the United States.
Tarmac delay means the holding of an aircraft on the ground either before taking off or after landing with no opportunity for its passengers to deplane.