Domestic operation
(1) Airplanes:
(i) Turbojet-powered airplanes;
(ii) Airplanes having a passenger-seat configuration of more than 9 passenger seats, excluding each crewmember seat; or
(iii) Airplanes having a payload capacity of more than 7,500 pounds.
(2) Locations:
(i) Between any points within the 48 contiguous States of the United States or the District of Columbia; or
(ii) Operations solely within the 48 contiguous States of the United States or the District of Columbia; or
(iii) Operations entirely within any State, territory, or possession of the United States; or
(iv) When specifically authorized by the Administrator, operations between any point within the 48 contiguous States of the United States or the District of Columbia and any specifically authorized point located outside the 48 contiguous States of the United States or the District of Columbia.
Source: 14 CFR Federal Aviation Regulations §110.2