From The Airport Wiki

The Boeing 737 is an American short to medium range, single aisle, narrow body jet airliner. With over 7,000 ordered and over 5,000 delivered, it is the most ordered and produced commercial passenger jet of all time and has been continuously manufactured by Boeing since 1967. The 737 is now so widely used that at any given time, there are over 1,250 airborne worldwide.[2] On average, somewhere around the world, a 737 takes off or lands every five seconds.