With a charter flight, you rent the entire aircraft, rather than just one seat. The aircraft can be large or small, and flights can be one-way or round-trip. The charter could be made on a flight-only basis, might include ground services such as transportation to or from meetings or could be part of a complete vacation package. Charter flights offer more flexibility than scheduled flights, with a wider choice of destinations and tailor-made itineraries.
Though the early Lockheed Jetstar had four, most production business jets have two jet engines, mostly rear-mounted podded engine. If mounted below their low wing, it wouldn't allow sufficient engine clearance without a too long landing gear. The HondaJet is the exception with its over the wing engine pods. Dassault Falcon still builds three-engine models derived from the Falcon 50, and the very light jet market has seen several single-engine design concepts and the introduction of the Cirrus Vision SF50 in 2016.