I think they mean a monotonous musical note
http://en.wikipedia.org/wiki/Drone_%28music%29 
But really, I'd assume quadcopters and hexacopter style drones. To get started and just gain a bit of experience why not pick up a Parrot AR Drone? Quite honestly you'd have a hard time building a reliable quadcopter for less money, and you can do a few hacks to this one to make it more programmable.
http://dronehacks.com/
You might even want to include a unit on terminology and discuss how the term "drone" compares to the term "UAV"
http://en.wikipedia.org/wiki/Unmanned_aerial_vehicle Both include fixed wing aircraft as well as rotary, and there is a lot of stuff you can do with the fixed wing planes as well.
Personally I don't have a lot of experience with building rotary UAVs with students, but fixed wing aircraft can be reasonably priced. I did tethered electric airplanes with my junior students and radio controlled "foamies" with my seniors.
Jason
Jason