Also: Repositioning flight, Positionierungsflug
Private jets are not always where a client wants to depart. If someone books a flight from Geneva but the suitable aircraft is in Munich, it first flies empty to Geneva. That leg is the positioning flight.
With a standard one-way charter, positioning costs are often built into the price. This is why a single sector can cost more than the flight time alone would suggest.
Positioning flights are one of the main sources of empty legs. Travellers with flexible schedules can fly on these sectors and benefit from the fact that the flight is taking place regardless.