‘Category A with respect to helicopters’ means a multi-engined helicopter designed with engine and system isolation features specified in the applicable
airworthiness codes and capable of operations using take-off and landing data
scheduled under a critical engine failure concept that assures adequate designated surface area and adequate performance capability for continued safe flight or safe rejected take-off in the event of engine failure.
‘Category B with respect to helicopters’ means a single-engined or multi-engined
helicopter that does not meet Category A standards.
Category B helicopters have no guaranteed capability to continue safe flight in the event of an engine failure, and unscheduled landing is assumed.
https://easa.europa.eu/agency-measur...Regulation.pdf