Though they are popularly called drones, the technical name for the drones is unmanned aerial vehicles (UAV). Any machine which is designed for flying in the air with human beings is likely to be more expensive as a lot of safety features have to be inbuilt in the machine to prevent loss of life or injuries. The technology used in drones is an extension of the technology used in remote controlled toys, especially remote controlled helicopters and planes.
As wireless control technologies became more advanced and inexpensive, it was possible to develop drones for military and commercial applications. They were initially used for military applications, however they are becoming increasingly popular among civilians for taking photos, making videos and in some cases, delivery of items in some areas.
However the use of the drones is restricted or highly regulated in many countries.