Drones are army planes that can fly for hours and probably weight hundreds if not thousands of pounds... Quadcopters are toys that can fly for minutes and weight only a few pounds...
All UAVs are drones and all drones are UAVs. Not all drones are quadcopters but all quadcopters are drones. Even in the strictest definition, what we commonly call "R/C Planes/Helicopters" actually qualify as "drones."
Well, not all of them.
https://en.wikipedia.org/wiki/George_de_Bothezat
http://3.bp.blogspot.com/-9v0ADuoE1cY/VHsBwdH-YGI/AAAAAAAAAh...