Name of president's Jet

The plane used to transport the President is always called Air Force One, irrespective of which particular plane he's in. It is generally a Boeing 747-200 modified with special equipment such in-flight refueling.

To be more technical, it is Air Force One if he is on an Air Force Plane, Marine One when he is on the helicopter, or Navy One if he is on a Navy plane. The "one" gives the aircraft priority in aviation hierarchy (the smaller the number, the higher the priority).