Is there a name for the area for aircraft to back track near the runway threshold? Some airports have an area, on the threshold, used to back track the aircraft, mainly because of the their wingspan, they look like a half wheel.
Is there any designation for this area?
It sounds like you're talking about these:



I'm not sure if the designation is "official", but pilots in the US (and the FAA in various documents) usually refer to such areas as a "Runway Turnaround Area" or simply "Runway Turnaround".
Their purpose is to allow aircraft which have back-taxied on the runway (or landed and rolled past the taxiway turn-offs) to turn around to position for take-off or return to a taxiway turn-off.



Note that the "runway turnaround" is distinct from a "run-up area": The runway turnaround is considered to be part of the runway, so an aircraft occupying that area is occupying the runway. A run-up area is generally a distinct area, usually off a taxiway, where aircraft can perform engine run-ups prior to entering the runway.