My dad was an aero space engineer, and I always had trouble with this. It is the speed you need to be going at, to not be pulled back by gravity. As a kid, I always thought, well big deal, if I am in a plane and just keep going up, eventually I will be out. The key I always missed was the velocity at that point was with no added power. So when the engine cuts off, what is your velocity? Is it enough to escape? Or do you need more power. Of course there is a good chance I still do not understand it.