14 C.F.R. § 262.2
As used in this part:
Air carrier means a citizen of the United States undertaking by any means, directly or indirectly, to provide air transportation.
Break in journey means any deliberate interruption by a passenger of a journey between a point in the United States and a point in a foreign country where there is a stopover at a foreign point scheduled to exceed 24 hours. If the stopover is 24 hours or less, whether it is a break in journey depends on various factors such as whether the segment between two foreign points and the segment between a foreign point and the United States were purchased in a single transaction and as a single ticket/itinerary, whether the segment between two foreign points is operated or marketed by a carrier that has no codeshare or interline agreement with the carrier operating or marketing the segment to or from the United States, and whether the stopover at a foreign point involves the passenger picking up checked baggage, leaving the airport, and continuing the next segment after a substantial amount of time.
Covered carrier means an air carrier or a foreign air carrier operating to, from or within the United States, conducting scheduled passenger service.
Covered flight means a scheduled flight operated or marketed by a covered carrier to, from, or within the United States, including itineraries with brief and incidental stopover(s) at a foreign point without a break in journey.
Licensed treating medical professional means an individual, including a physician, a nurse practitioner, a physician's assistant, or other medical provider, who is licensed or authorized under the law of a State or territory in the United States or a comparable jurisdiction in another country to engage in the practice of medicine to diagnose or treat a patient for a health condition that is the reason for the passenger to request a travel credit or voucher under § 262.4(b) and (c).
Merchant of record means the entity (carrier or ticket agent) responsible for processing payment by the consumer for airfare or ancillary services or products, as shown in the consumer's financial charge statements such as debit or credit card charge statements.
Foreign air carrier means a person, not a citizen of the United States, undertaking by any means, directly or indirectly, to provide foreign air transportation.
Public health emergency has the same meaning as defined in 42 CFR 70.1 .
Serious communicable disease means a communicable disease as defined in 42 CFR 70.1 that can cause serious health consequences (e.g., breathing problems, organ damage, neurological difficulties, death) and can be easily transmitted by casual contact in an aircraft cabin environment (i.e., easily spread to others in an aircraft cabin through general activities of passengers such as sitting next to someone, shaking hands, talking to someone, or touching communal surfaces). For example, the common cold is readily transmissible in an aircraft cabin environment but does not have severe health consequences. AIDS has serious health consequences but is not readily transmissible in an aircraft cabin environment. Both the common cold and AIDS would not be considered serious communicable diseases for purposes of this part. SARS is readily transmissible in an aircraft cabin environment and has severe health consequences. SARS would be considered a serious communicable disease for purposes of this part.
14 C.F.R. §262.2