What is the difference between a business jet and a regional jet?
I would say its not quite who operates but how its operated. A business jet is typically outfitted to carry a small number of people in a very luxurious way while a regional jet is outfitted to carry a lot of people a short distance.

No one even says business jets have to be small or of a select list of airframes, you can order a 747 business jet if you have the cash. Similarly no one says a regional jet has to be small, we are now seeing 747SR's doing short haul flights in Japan.



From a legal standpoint, the difference may be in the operation type as well. Scheduled regional flights here in the US will occur under part 121 while charter business operations will generally occur under part 135 if you own the plane the operation may even occur under part 91. This mainly has differences on inspection intervals for the airframe and some other operational related things. Assuming you can land the plane on the runway and depart again safely these don't limit where you can go.