It refers to the standards and recommended practices (SARPS) issued by ICAO for aircraft (such as the Airbus A300, A310, A320, A330 and A350, the Boeing 737, 757, 767, 777, 787, the Embraer E-Jets, and the ATR 72) to fly long-distance routes that were previously off-limits to twin-engined aircraft.
*"History & Development of the Boeing 737", b737.org.uk, October 23, 2005