Cabotage
Cabotage rules restrict foreign-registered aircraft or foreign operators from carrying paying passengers between two points inside another country. A US-registered charter jet may fly New York to Paris, but it generally cannot then sell a Paris–Nice sector; likewise an EU operator cannot pick up a paying passenger in Miami and fly them to Aspen. Some countries grant exemptions with prior approval, and private (non-revenue) flights with the same passengers are usually allowed. Cabotage matters when you plan a multi-city trip abroad: the operator may need to use a local aircraft for domestic legs, or price the whole itinerary as one international journey with the same passengers throughout.