There are 3 general terms for these vehicles:
Unmanned Aerial Vehicle (UAV)
Remotely Piloted Aircraft (RPA)
Unmanned Air Systems (UAS)
and they describe any flying vehicle or system that does not contain a human inside it.
They may or may not have a pilot guiding it physically through the air.
Many UAV's are given orders to linger, seek and loiter, seek and hunt, document, detect, fly between predetermined waypoints (a spot on the Earth described by its GPS coordinates) and many other commands that allow the vehicle to make decisions on its own without the guidance of a human.
There is no distinction in these terms for type of aircraft in terms of number and type of propellers, or motors or size.
People that use these aircraft for their job, military, police, or search and rescue for example, never use the word drone, citing the need to mitigate fear and confusion, and lack of acronym.
The best meaning for drone is a flying vehicle, unmanned, made to find people and places on its own and fire weapons to kill and destroy.
It is used however, as anything that flies and is remotely controlled or can fly autonomously. It is used by the media to spread fear of technology and the unknown to get attention, spread controversy and increase ratings. Autonomous vehicle would be better, but if it doesn't fly itself, it's just an RC airplane or helicopter, as quad- or any multi-bladed copter is a type of rotorcraft or helicopter.