Jet pack, rocket belt, rocket pack, and similar names, are various types of device, usually worn on the back, that use jets of escaping gases (or in some cases liquid water) to allow a single user to fly. It is a personal aircraft that requires minimal training with a goal to create a Segway for the sky, where the principles of flying would be very simple .
The concept of these devices emerged from science fiction in the 1920s and popularised in the 1960s as the technology became a reality. Currently, the only practical use of the jet pack has been extra-vehicular activity for astronauts. Despite decades of advancement in the technology, the challenges of Earth's atmosphere, Earth's gravity, and the human body (which is not well suited for this type of flight) remain an obstacle to its potential use in the military and as a means of personal transport. There's a lot more engineering in it than one might perceive. The key problem has been what is called the "weight-to-thrust" ratio, which basically boils down to the conundrum that the heavier you are or the longer you want to stay in the air, the more power you need, which in turn means you have to carry more weight. It’s been a long time coming, but the future is here! Finally we can all take flight as Martin Aircraft in New Zealand releases the first commercially-available jet pack!