14 C.F.R. § 257.3
As used in this part:
Air transportation means foreign air transportation or interstate air transportation as defined in 49 U.S.C. 40102(a)(23) and (25) respectively.
Carrier means any air carrier or foreign air carrier as defined in 49 U.S.C. 40102(2) or 49 U.S.C. 40102(21) , respectively, that is engaged directly in scheduled passenger air transportation, including by wet lease.
Code-sharing arrangement means an arrangement whereby a carrier's designator code is used to identify a flight operated by another carrier.
Designator code means the airline designations originally allotted, administered, and prescribed by the Department of Transportation (DOT), by operation of law, pursuant to 49 U.S.C. Subtitle VII or its predecessor's statutory provisions still in effect by law.
Long-term wet lease means a lease by which the lessor provides both an aircraft and crew dedicated to a particular route(s), and which either:
Operating carrier means the carrier that is operating the aircraft in a code-sharing arrangement or long-term wet lease.
Ticket agent has the meaning ascribed to it in 49 U.S.C. 40102(45) .
14 C.F.R. §257.3