The meaning is easily clear from the name. These are the devices used to deliver material with the help of drone. These are automated devices that can deliver goods without the help of a man.
This is a still emerging technology.In the United States initial attempts at commercial use of Delivery drone, such as the Tacocopter company for food delivery, were blocked by FAA regulation. As of 2015, delivering of packages with drones in the United States is not permitted. On the 13th March 2015, in Sheffield, FPS Distribution completed the first commercial delivery using a Delivery drone.
Drug cartels have used Delivery drone to transport contraband, sometimes using GPS-guided Delivery drone.