Where does space start? Where does it end? Is it unlimited? Does it have boundaries? How can we define space? A practical, yet precise definition of space is difficult to come up with. Let me give it a try, though: I would say that space includes all regions in the Universe where a free trajectory of a spacecraft, or of any natural object such as a planet, an asteroid or a comet, is possible, with no or with minimum braking force due to a drag-producing medium such as an atmosphere.