Barnsley chop is the traditional name in United Kingdom. Elsewhere, butchers sell the same piece — or a close cousin — under a different name.
Same anatomical cut from the saddle, but Barnsley chop is cut across both loin eyes plus the spinal bone — a single chop spanning both sides of the animal — while a standard loin chop is cut from one side only.
Both are British grill chops; the Barnsley is a double loin chop, so it is leaner and larger than the chump.