En dehors is a classical ballet term meaning “outward.” En dehors is added to other steps and terms to describe which way a step should be moving.
For example, a pirouette en dehors would mean that the dancer would turn “outward” away from the supporting leg.
Another way to think of en dehors is “from the front to the back.” A rond de jambe en dehors would have the dancer start to the front and move their outwards to the side and then to the back in a circular motion.